Joining methods for ceramic composite bodies

ABSTRACT

This invention relates generally to a novel method for joining at least one first self-supporting body to at least one second self-supporting body which is similar in composition to or different in composition from said at least one first self-supporting body and to novel products which result from such joining. In some of its more specific aspects, this invention relates to different techniques for joining ceramic matrix composite bodies to other ceramic matrix composite bodies of similar characteristics and for joining ceramic matrix composite bodies to bodies which have different characteristics (e.g., metals). The ceramic matrix composite bodies of this invention are produced by a reactive infiltration of a molten parent metal into a bed or mass containing at least one of a boron source material, a carbon source material, and a nitrogen source material and, optionally, one or more inert fillers.

This is a c-i-p of Ser. No. 589,634, filed Sep. 28, 1990, which is ac-i-p of Ser. No. 551,749, filed Jul. 12, 1990, both now abandoned.

TECHNICAL FIELD

This invention relates generally to a novel method for joining at leastone first self-supporting body, to at least one second self-supportingbody which is similar in composition to or different in composition fromsaid at least one first self-supporting body .and to novel productswhich result from such joining. In some of its more specific aspects,this invention relates to different techniques for joining ceramicmatrix composite bodies to other ceramic matrix composite bodies ofsimilar characteristics and for joining ceramic matrix composite bodiesto bodies which have different characteristics (e.g., metals). Theceramic matrix composite bodies of this invention are produced by areactive infiltration of a molten parent metal into a bed or masscontaining a boron source material and a carbon source material (e.g.,boron carbide) and/or a boron source material and a nitrogen sourcematerial (e.g., boron nitride) and, optionally, one or more inertfillers.

BACKGROUND ART

In recent years, there has been an increasing interest in the use ofceramics for structural applications historically served by metals. Theimpetus for this interest has been the superiority of ceramics withrespect to certain properties, such as corrosion resistance, hardness,wear resistance, modulus of elasticity, and refractory capabilities whencompared with metals.

However, a major limitation on the use of ceramics for such purposes isthe feasibility and cost of producing the desired ceramic structures.For example, the production of ceramic boride bodies by the methods ofhot pressing, reaction sintering and reaction hot pressing is wellknown. In the case of hot pressing, fine powder particles of the desiredboride are compacted at high temperatures and pressures. Reaction hotpressing involves, for example, compacting at elevated temperatures andpressures boron or a metal boride with a suitable metal-containingpowder. U.S. Pat. No. 3,937,619 to Clougherty describes the preparationof a boride body by hot pressing a mixture of powdered metal with apowdered diboride, and U.S. Pat. No. 4,512,946 to Brun describes hotpressing ceramic powder with boron and a metal hydride to form a boridecomposite.

However, these hot pressing methods require special handling andexpensive special equipment, they are limited as to the size and shapeof the ceramic part produced, and they typically involve low processproductivities and high manufacturing costs.

A second major limitation on the use of ceramics for structuralapplications is their general lack of toughness (i.e. damage toleranceor resistance to fracture). This characteristic tends to result insudden, easily induced, catastrophic failure of ceramics in applicationsinvolving even rather moderate tensile stresses. This lack of toughnesstends to be particularly common in monolithic ceramic boride bodies.

One approach to overcome this problem has been to attempt to useceramics in combination with metals, for example, as cermets or metalmatrix composites. The objective of this approach is to obtain acombination of the best properties of the ceramic (e.g. hardness and/orstiffness) and the metal (e.g. ductility). U.S. Pat. No, 4,585,618 toFresnel, et al., discloses a method of producing a cermet whereby a bulkreaction mixture of particulate reactants, which react to produce asintered self-sustaining ceramic body, is reacted while in contact witha molten metal. The molten metal infiltrates at least a portion of theresulting ceramic body. Exemplary of such a reaction mixture is onecontaining titanium, aluminum and boron oxide (all in particulate form),which is heated while in contact with a pool of molten aluminum. Thereaction mixture reacts to form titanium diboride and alumina as theceramic phase, which is infiltrated by the molten aluminum. Thus, thismethod uses the aluminum in the reaction mixture principally as areducing agent. Further, the external pool of molten aluminum is notbeing used as a source of precursor metal for a boride forming reaction,but rather it is being utilized as a means to fill the pores in theresulting ceramic structure. This creates cermets which are wettable andresistant to molten aluminum. These cermets are particularly useful inaluminum production cells as components which contact the moltenaluminum produced but preferably remain out of contact with the moltencryolite.

European Patent Application Publication No. 0,113,249 to Reeve, et al.discloses a method for making a cermet by first forming in situdispersed particles of a ceramic phase in a molten metal phase, and thenmaintaining this molten condition for a time sufficient to effectformation of an intergrown ceramic network. Formation of the ceramicphase is illustrated by reacting a titanium salt with molten metal suchas aluminum. A ceramic boride is developed in situ and becomes anintergrown network. There is, however, no infiltration, and further theboride is formed as a precipitate in the molten metal. Both examples inthe application expressly state that no grains were formed of TiAl₃,AlB₂, or AlB₁₂, but rather TiB₂ is formed demonstrating the fact thatthe aluminum is not the metal precursor to the boride.

U.S. Pat. No. 3,864,154 to Gazza, et al. discloses a ceramic-metalsystem produced by infiltration. An AlB₁₂ compact was impregnated withmolten aluminum under vacuum to yield a system of these components.Other materials prepared included SiB₆ -Al, B-Al; B₄ C-Al/Si; and AlB₁₂-B-Al. There is no suggestion whatsoever of a reaction, and nosuggestion of making composites involving a reaction with theinfiltrating metal nor of any reaction product embedding an inert filleror being part of a composite.

U.S. Pat. No. 4,605,440 to Halverson, et al., discloses that in order toobtain B₄ C-Al composites, a B₄ C-Al compact (formed by cold pressing ahomogeneous mixture of B₄ C and Al powders) is subjected to sintering ineither a vacuum or an argon atmosphere. There is no infiltration ofmolten metal from a pool or body of molten precursor metal into apreform. Further, there is no mention of a reaction product embedding aninert filler in order to obtain composites utilizing the favorableproperties of the filler.

While these concepts for producing cermet materials have in some casesproduced promising results, there is a general need for more effectiveand economical methods to prepare boride-containing materials.

DESCRIPTION OF COMMONLY OWNED U.S. PATENTS AND PATENT APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/589,634, filed on Sep. 28, 1990, as a continuation-in-partof U.S. patent application Ser. No. 07/551,749, filed on Jul. 12, 1990,both in the names of James Cheng-Koung Wang et al. and both entitled "AMethod For Joining Ceramic Composite Bodies and Articles FormedThereby". The disclosure of both of the above-identified patentapplications is hereby expressly incorporated by reference.

Many of the above-discussed problems associated with the production ofboride-containing materials have been addressed in U.S. Pat. No.4,885,130 (hereinafter "Patent '130"), which issued on Dec. 5, 1989, inthe names of Terry Dennis Claar et al., and is entitled "Process forPreparing Self-Supporting Bodies and Products Produced Thereby".

Briefly summarizing the disclosure of Patent '130, self-supportingceramic bodies are produced by utilizing a parent metal infiltration andreaction process (i.e., reactive infiltration) in the presence of a masscomprising boron carbide. Particularly, a bed or mass comprising boroncarbide and, optionally, one or more of a boron donor material and acarbon donor material, is infiltrated by molten parent metal, and thebed may be comprised entirely of boron carbide or only partially ofboron carbide, thus resulting in a self-supporting body comprising, atleast in part, one or more parent metal boron-containing compounds,which compounds include a parent metal boride or a parent metal borocarbide, or both, and typically also may include a parent metal carbide.It is also disclosed that the mass comprising boron carbide which is tobe infiltrated may also contain one or more inert fillers mixed with theboron carbide. Accordingly, by combining an inert filler, the resultwill be a composite body having a matrix produced by the reactiveinfiltration of the parent metal, said matrix comprising at least oneboron-containing compound, and the matrix may also include a parentmetal carbide, the matrix embedding the inert filler. It is furthernoted that the final composite body product in either of theabove-discussed embodiments (i.e., filler or no filler) may include aresidual metal (e.g., at least one metallic constituent of the originalparent metal).

Broadly, in the disclosed method of Patent '130, a mass comprising boroncarbide and, optionally, one or more of a boron donor material and acarbon donor material, is placed adjacent to or in contact with a bodyof molten metal or metal alloy, which is melted in a substantially inertenvironment within a particular temperature envelope. The molten metalinfiltrates the mass comprising boron carbide and reacts with at leastthe boron carbide to form at least one reaction product. The boroncarbide (and/or the boron donor material and/or the carbon donormaterial) is reduced, at least in part, by the molten parent metal,thereby forming the parent metal boron-containing compound (e.g., aparent metal boride and/or boro compound under the temperatureconditions of the process). Typically, a parent metal carbide is alsoproduced, and in certain cases, a parent metal boro carbide is produced.At least a portion of the reaction product is maintained in contact withthe metal, and molten metal is drawn or transported toward the unreactedmass comprising boron carbide by a wicking or capillary action. Thistransported metal forms additional parent metal boride, carbide, and/orboro carbide and the formation or development of a ceramic body iscontinued until either the parent metal or mass comprising boron carbidehas been consumed, or until the reaction temperature is altered to beoutside of the reaction temperature envelope. The resulting structurecomprises one or more of a parent metal boride, a parent metal borocompound, a parent metal carbide, a metal (which, as discussed in Patent'130, is intended to include alloys and intermetallics), or voids, orany combination thereof. Moreover, these several phases may or may notbe interconnected in one or more dimensions throughout the body. Thefinal volume fractions of the boron-containing compounds (i.e., borideand boron compounds), carbon-containing compounds, and metallic phases,and the degree of interconnectivity, can be controlled by changing oneor more conditions, such as the initial density of the mass comprisingboron carbide, the relative amounts of boron carbide and parent metal,alloys of the parent metal, dilution of the boron carbide with a filler,the amount of boron donor material and/or carbon donor material mixedwith the mass comprising boron carbide, temperature, and time.Preferably, conversion of the boron carbide to the parent metal boride,parent metal boro compound(s) and parent metal carbide is at least about50%, and most preferably at least about 90%.

The typical environment or atmosphere which is utilized in Patent '130is one which is relatively inert or unreactive under the processconditions. Particularly, it is disclosed that an argon gas, or avacuum, for example, would be suitable process atmospheres. Stillfurther, it is disclosed that when zirconium is used as the parentmetal, the resulting composite comprises zirconium diboride, zirconiumcarbide, and residual zirconium metal. It is also disclosed that whenaluminum parent metal is used with the process, the result is analuminum boro carbide such as Al₃ B₄ 8C₂, AlB₁₂ C₂ and/or AlB₂₄ C₄, withaluminum parent metal and other unreacted unoxidized constituents of theparent metal remaining. Other parent metals which are disclosed as beingsuitable for use with the processing conditions included silicon,titanium, hafnium, lanthanum, iron, calcium, vanadium, niobium,magnesium, and beryllium.

Still further, it is disclosed that by adding a carbon donor material(e.g., graphite powder or carbon black) and/or a boron donor material(e.g., a boron powder, silicon burides, nickel burides and iron burides)to the mass comprising boron carbide, the ratio of parentmetal-boride/parent metal-carbide can be adjusted. For example, ifzirconium is used as the parent metal, the ratio of ZrB₂ /ZrC can bereduced if a carbon donor material is utilized (i.e., more ZrC isproduced due to the addition of a carbon donor material in the mass ofboron carbide) while if a boron donor material is utilized, the ratio ofZrB₂ /ZrC can be increased (i.e., more ZrB₂ is produced due to theaddition of a boron donor material in the mass of boron carbide). Stillfurther, the relative size of the ZrB₂ platelets which are formed in thebody may be larger than platelets that are formed by a similar processwithout the use of a boron donor material. Thus, the addition of acarbon donor material and/or a boron donor material may also effect themorphology of the resultant material.

In another related Patent, specifically, U.S. Pat. No. 4,915,736(hereinafter referred to as "Patent '736"), issued in the names of TerryDennis Claar and Gerhard Hans Schiroky, on Apr. 10, 1990, and entitled"A Method of Modifying Ceramic Composite Bodies By a CarburizationProcess and Articles Produced Thereby", additional modificationtechniques are disclosed. Specifically, Patent '736 discloses that aceramic composite body made in accordance with the teachings of, forexample, Patent '130 can be modified by exposing the composite to agaseous carburizing species. Such a gaseous carburizing species can beproduced by, for example, embedding the composite body in a graphiticbedding and reacting at least a portion of the graphitic bedding withmoisture or oxygen in a controlled atmosphere furnace. However, thefurnace atmosphere should comprise typically, primarily, a non-reactivegas such as argon. It is not clear whether impurities present in theargon gas supply the necessary O₂ for forming a carburizing species, orwhether the argon gas merely serves as a vehicle which containsimpurities generated by some type of volatilization of components in thegraphitic bedding or in the composite body. In addition, a gaseouscarburizing species could be introduced directly into a controlledatmosphere furnace during heating of the composite body.

Once the gaseous carburizing species has been introduced into thecontrolled atmosphere furnace, the setup should be designed in such amanner to permit the carburizing species to be able to contact at leasta portion of the surface of the composite body buried in the looselypacked graphitic powder. It is believed that carbon in the carburizingspecies, or carbon from the graphitic bedding, will dissolve into theinterconnected zirconium carbide phase, which can then transport thedissolved carbon throughout substantially all of the composite body, ifdesired, by a vacancy diffusion process. Moreover, Patent '736 disclosesthat by controlling the time, the exposure of the composite body to thecarburizing species and/or the temperature at which the carburizationprocess occurs, a carburized zone or layer can be formed on the surfaceof the composite body. Such process could result in a hard,wear-resistant surface surrounding a core of composite material having ahigher metal content and higher fracture toughness.

Thus, if a composite body was formed having a residual parent metalphase in the amount of between about 5-30volume percent, such compositebody could be modified by a post-carburization treatment to result infrom about 0 to about 2 volume percent, typically about 1/2 to about 2volume percent, of parent metal remaining in the composite body.

U.S. Pat. No. 4,885,131 (hereinafter "Patent '131"), issued in the nameof Marc S. Newkirk on Dec. 5, 1989, and entitled "Process For PreparingSelf-Supporting Bodies and Products Produced Thereby", disclosesadditional reactive infiltration formation techniques. Specifically,Patent '131 discloses that self-supporting bodies can be produced by areactive infiltration of a parent metal into a mixture of a bed or masscomprising a boron donor material and a carbon donor material. Therelative amounts of reactants and process conditions may be altered orcontrolled to yield a body containing varying volume percents ofceramic, metals, and/or porosity and varying ratios of one ceramicconstituent to another ceramic constituent.

In another related patent application, specifically, copending

U.S. patent application Ser. No. 07/296,770 (hereinafter referred to as"Application '770"), filed in the names of Terry Dennis Claar et al., onJan. 13, 1989, and entitled "A Method of Producing Ceramic CompositeBodies", additional reactive infiltration formation techniques aredisclosed. Specifically, Application '770 discloses various techniquesfor shaping a bed or mass comprising boron carbide into a predeterminedshape and thereafter reactively infiltrating the bed or mass comprisingboron carbide to form a self-supporting body of a desired size andshape.

U.S. Pat. No. 5,011,063, which issued on Apr. 30, 1991, in the name ofTerry Dennis Claar, as a continuation of U.S. patent application Ser.No. 07/296,837, filed in the name of Terry Dennis Claar on Jan. 13,1989, and entitled "A Method of Bonding A Ceramic Composite Body to aSecond Body and Articles Produced Thereby", discloses various bondingtechniques for bonding self-supporting bodies to second materials.Particularly, this patent discloses that a bed or mass comprising one ormore boron-containing compounds is reactively infiltrated by a moltenparent metal to produce a self-supporting body. Moreover, residual orexcess metal is permitted to remain bonded to the formed self-supportingbody. The excess metal is utilized to form a bond between the formedself-supporting body and another body (e.g., a metal body or a ceramicbody of any particular size or shape).

The reactive infiltration of a parent metal into a bed or masscomprising boron nitride is disclosed in U.S. Pat. No. 4,904,446(hereinafter "Patent '446"), issued in the names of Danny Ray White etal., on Feb. 27, 1990, and entitled "Process for PreparingSelf-Supporting Bodies and Products Made Thereby". Specifically, thispatent discloses that a bed or mass comprising boron nitride can bereactively infiltrated by a parent metal. The relative amount ofreactants and process conditions may be altered or controlled to yield abody containing varying volume percents of ceramic, metal and/orporosity. The resulting self-supporting body comprises aboron-containing compound, a nitrogen-containing compound and,optionally, a metal. Additionally, inert fillers may be included in theformed self-supporting body.

A further post-treatment process for modifying the properties ofproduced ceramic composite bodies is disclosed in U.S. Pat. No.5,004,714, which issued in the names of Terry Dennis Claar et al., onApr. 2, 1991, and is entitled "Method of Modifying Ceramic CompositeBodies By A Post-Treatment Process and Articles Produced Thereby".Specifically, this patent discloses that self-supporting bodies producedby a reactive infiltration technique can be post-treated by exposing theformed bodies to one or more metals and heating the exposed bodies tomodify at least one property of the previously formed composite body.One specific example of a post-treatment modification step includesexposing a formed body to a siliconizing environment.

U.S. Pat. No. 5,019,539, which issued in the names of Terry Dennis Claaret al., on May 28, 1991, and is entitled "Process for PreparingSelf-Supporting Bodies Having Controlled Porosity and Graded Propertiesand Products Produced Thereby", discloses reacting a mixture of powderedparent metal with a bed or mass comprising boron carbide and,optionally, one or more inert fillers. Additionally, it is disclosedthat both a powdered parent metal and a body or pool of molten parentmetal can be induced to react with a bed or mass comprising boroncarbide. The body which is produced is a body which has controlled orgraded properties.

The disclosures of each of the above-discussed Commonly Owned U.S.patent applications and patents are herein expressly incorporated byreference.

SUMMARY OF THE INVENTION

In accordance with a first step of the present invention,self-supporting ceramic bodies are produced by utilizing a parent metalinfiltration and reaction process (i.e. reactive infiltration) in thepresence of a bed or mass comprising, for example, boron carbide orboron nitride. Such bed or mass is infiltrated by molten parent metal,and the bed may be comprised entirely of boron carbide, boron nitride,and/or mixtures of boron donor materials, carbon donor materials and/ornitrogen donor materials. Depending on the particular reactants involvedin the reactive infiltration, the resulting bodies which are producedcomprise one or more reaction products such as parent metalboron-containing compounds, parent metal carbon-containing compounds,parent metal nitrogen-containing compounds, etc. Alternatively, the massto be infiltrated may contain one or more inert fillers admixedtherewith to produce a composite by reactive infiltration, whichcomposite comprises a matrix of one or more of the aforementionedreaction products and the matrix also may include residual unreacted orunoxidized constituents of the parent metal. The filler material may beembedded by the formed matrix. Regardless of whether a filler materialis used, the final product may include a metal (e.g., one or moremetallic constituents of the parent metal). Still further, in some casesit may be desirable to add a carbon donor material (i.e., acarbon-containing compound) and/or a boron donor material (i.e., aboron-containing compound) and/or a nitrogen-donor material (i.e., anitrogen-containing compound) to the bed or mass which is to beinfiltrated to modify, for example, the relative amounts of one formedreaction product to another, thereby modifying resultant mechanicalproperties of the composite body. Still further, the reactantconcentrations and process conditions may be altered or controlled toyield a body containing varying volume percents of ceramic compounds,metal and/or porosity.

Broadly, in accordance with the first step of the method according tothis invention, the bed or mass which is to be reactively infiltratedmay be placed adjacent to or contacted with a body of molten metal ormetal alloy, which is melted in a substantially inert environment withina particular temperature envelope. The molten metal infiltrates the massand reacts with at least one constituent of the bed or mass to beinfiltrated to form one or more reaction products. At least a portion ofthe formed reaction product is maintained in contact with the metal, andmolten metal is drawn or transported toward the remaining unreacted massby a wicking or capillary action. This transported metal formsadditional reaction product upon contact with the remaining unreactedmass, and the formation or development of a ceramic body is continueduntil the parent metal or remaining unreacted mass has been consumed, oruntil the reaction temperature is altered to be outside the reactiontemperature envelope. The resulting structure comprises, depending uponthe particular materials comprising the bed or mass which is to bereactively infiltrated, one or more of a parent metal boride, a parentmetal boro compound, a parent metal carbide, a parent metal nitride, ametal (which as used herein is intended to include alloys andintermetallics), or voids, or a combination thereof, and these severalphases may or may not be interconnected in one or more dimensions. Thefinal volume fractions of the reaction products and metallic phases, andthe degree of interconnectivity, can be controlled by changing one ormore conditions, such as the initial density of the mass which is to bereactively infiltrated, the relative amounts and chemical composition ofthe materials contained within the mass which is to be reactivelyinfiltrated, the amount of parent metal provided for reaction, thecomposition of the parent metal, the presence and amount of one or morefiller materials, temperature, time, etc.

Typically, the mass to be reactively infiltrated should be at leastsomewhat porous so as to allow for wicking of the parent metal throughthe reaction product. Wicking occurs apparently either because anyvolume change on reaction does not fully close off pores through whichparent metal can continue to wick, or because the reaction productremains permeable to the molten metal due to such factors as surfaceenergy considerations which render at least some of its grain boundariespermeable to the parent metal.

In another aspect of the first step of the-invention, a composite isproduced by the transport of molten parent metal into the bed or masswhich is to be reactively infiltrated which has admixed therewith one ormore inert filler materials. In this embodiment, one or more suitablefiller materials are mixed with the bed or mass to be reactivelyinfiltrated. The resulting self-supporting ceramic-metal composite thatis produced typically comprises a dense microstructure which comprises afiller embedded by a matrix comprising at least one parent metalreaction product, and also may include a substantial quantity of metal.Typically, only a small amount of material (e.g., a small amount ofboron carbide) is required to promote the reactive infiltration process.Thus, the resulting matrix can vary in content from one composedprimarily of metallic constituents thereby exhibiting certain propertiescharacteristic of the parent metal; to cases where a high concentrationof reaction product is formed, which dominates the properties of thematrix. The filler may serve to enhance the properties of the composite,lower the raw materials cost of the composite, or moderate the kineticsof the reactions which produce the reaction product and the associatedrate of heat evolution. The precise starting amounts and composition ofmaterials utilized in the reaction infiltration process can be selectedso as to result in a desirable body which is compatible with the secondstep of the invention.

In another aspect of the first step of the present invention, thematerial to be reactively infiltrated is shaped into a preformcorresponding to the geometry of the desired final composite. Subsequentreactive infiltration of the preform by the molten parent metal resultsin a composite having the net shape or near net shape of the preform,thereby minimizing expensive final machining and finishing operations.Moreover, to assist in reducing the amount of final machining andfinishing operations, a barrier material can at least partially, orsubstantially completely, surround the preform. The use of a graphitematerial (e.g., a graphite mold, a graphite tape product, a graphitecoating, etc.) is particularly useful as a barrier for such parentmetals as zirconium, titanium, or hafnium, when used in combination withpreforms made of, for example, at least one of boron carbide, boronnitride, boron and carbon. Still further, by placing an appropriatenumber of through-holes having a particular size and shape in theaforementioned graphite mold, the amount of porosity which typicallyoccurs within a composite body manufactured according to the first stepof the present invention, can be reduced. Typically, a plurality ofholes is placed in a bottom portion of the mold, or that portion of themold toward which reactive infiltration occurs. The holes function as aventing means which permit the removal of, for example, argon gas whichhas been trapped in the preform as the parent metal reactiveinfiltration front infiltrates the preform.

Still further, the procedures discussed above herein in the Section"Description of Commonly Owned U.S. Patents and Patent Applications" maybe applicable in connection with the first step of the presentinvention.

Once a self-supporting body has been formed in accordance with the firststep of the present invention, the second step of the present inventionis put into effect. The second step of the present invention involves aplurality of different embodiments, each of which is discussed below.

In a first embodiment of the second step of the present invention, atleast one first self-supporting body formed in accordance with the firststep of the invention is contacted with at least one secondself-supporting body formed in accordance with the first step of theinvention, said contacting occurring with or without the application ofexternal pressure upon the contacted bodies. The contacted bodies arethen held together in an appropriate manner (e.g., by the force ofgravity, by some external pressure means, etc.) and are heated to anelevated temperature to permit the bodies to bond together. Stated morespecifically, when at least two bodies made in accordance with the firststep of the present invention are contacted with each other and areheated to a temperature which is above the melting point of at least aportion of the metallic constituent in at least one of the bodies andthe contacted bodies are held at such temperature for an appropriateamount of time and in the presence of, for example, a substantiallyinert atmosphere (e.g., an atmosphere similar to the formationatmosphere utilized in the first step of the present invention), saidcontacted bodies can bond together along at least a portion of the areaof mutual contact and form a well bonded unitary piece. The conditionsutilized to achieve the bond between said at least two contacted bodiescan be tailored so that the original joining area between said at leasttwo bodies is substantially completely indistinguishable from any otherarea in said at least two bodies. For example, if the temperatureutilized to join the bodies is a temperature only slightly above themelting point of at least a portion of the metallic constituent in atleast one of the bodies, the time required for joining may be longerthan the time required for joining when the temperature is significantlyabove the melting point of substantially all of the metallic constituentin both of the bodies.

The ability to join said at least two bodies together is a significantachievement because rather than forming a very complex-shaped preform ofa bed or mass which is to be reactively infiltrated or a complex-shapedmold to contain a bed or mass of filler material which is to bereactively infiltrated, a plurality of simpler or less complex shapedpreforms (or molds containing filler material) can be utilized to formself-supporting bodies in accordance with the first step of theinvention. Such formed bodies can thereafter be bonded together to forman intricate or complex-shaped piece or a very large piece. Due to thenature of the joining mechanism, it can be extremely difficult, if notimpossible, to distinguish any joint area from any other area of theformed body. Accordingly, this invention permits the formation ofintricate and complex shapes, as well as large bodies, by combining aplurality of relatively simple shapes made by relatively simpletechniques.

In a second embodiment of the second step of the present invention, theplurality of individual bodies which are bonded together do not consistentirely of materials made in accordance with the first step of thepresent invention. For example, materials such as metals, ceramics,etc., can be bonded to articles made in accordance with the first stepof the invention. In this second embodiment of the second step of theinvention, in order for bonding to occur, it can be desirable for sometype of reaction to occur between a body produced in accordance with thefirst step of the invention and a second body.

A third embodiment of the second step of the present invention involvesthe placement of materials, similar to those utilized to form theself-supporting body of the first step of the present invention, betweenat least two bodies which are to be bonded together. Specifically, thejoining area which exists between said at least two bodies which are tobe bonded together can be filled with, for example, a powdered parentmetal and a material which is to be reactively infiltrated.Alternatively, the joint can be filled with, for example, a materialwhich is to be reactively infiltrated and a source of parent metal canbe placed into contact with the material which is to be reactivelyinfiltrated. Thus, a reaction is permitted to occur between the parentmetal and the material which is to be reactively infiltrated so as toform a bonding zone at the joining area between the aforementioned atleast two bodies.

In accordance with the third embodiment of the second step of thepresent invention, if the bodies to be joined are of similar composition(e.g., two bodies of the same composition formed in accordance with thefirst step of the present invention), then the processing conditionsutilized to form the joint can be tailored so that the joining area issubstantially indistinguishable from other areas of the aforementionedbodies to be joined. However, if the bodies to be joined have a verydifferent composition, then the joining area will be distinguishable. Itshould be noted that bodies can be substantially different incomposition and can still be joined together by the methods of theabove-described third embodiment. For example, a body produced inaccordance with the first step of the present invention can be bondedto, for example, a metal.

In a fourth embodiment of the second step of the present invention, abrazing material in any suitable form is contacted with the bondingsurfaces of two bodies formed in accordance with the first step of thepresent invention or, alternatively, the brazing material may be placedin contact with the bonding surfaces of one body formed in accordancewith the first step of the present invention and a second body.Particularly, for example, a brazing material in the shape of a foil,rod, plate, paste or powder which comprises an active brazing metal oralloy (e.g.., an alloy comprising titanium) is placed in contact with atleast a portion of the bonding surfaces of at least two self-supportingbodies made in accordance with the first step of the present invention.Without wishing to be bound by any particular theory or explanation, itappears as though the active brazing metal or alloy assists in wettingand bonding the materials together. To achieve bonding by use of abrazing material, the contacted bodies, or at least the bonding surfacesof the contacted bodies which are in contact with the brazing material,are heated to a temperature which permits the active brazing metal oralloy contained in the brazing material to bond the bodies together.

In each of the above-discussed embodiments of the second step of thepresent invention, it may be desirable to bond together bodies made inaccordance with the first step of the invention. In this case, it ispossible that bodies produced in accordance with the first step of thepresent invention may comprise completely different parent metals andthus completely different reaction products. Alternatively, the bodiesmay have been produced by using very similar parent metals and thus thebodies may comprise very similar reaction products. Accordingly, thepresent invention permits bonding to occur between dissimilar materialsdue to the inherent nature of the bond which is formed. Thus, thepresent invention permits the formation of relatively complex shapesand/or relatively large shapes due to the ability to bond similar ordissimilar bodies together in a secure manner.

DEFINITIONS

As used in this specification and the appended claims, the terms beloware defined as follows:

"Parent metal" refers to that metal, e.g. zirconium, titanium, hafnium,etc., which is the precursor to the polycrystalline oxidation reactionproduct, that is, the parent metal boride, parent metal carbide, parentmetal nitride, or other parent metal compound, and includes that metalas a pure or relatively pure metal, a commercially available metalhaving impurities and/or alloying constituents therein, and an alloy inwhich that metal precursor is the major constituent; and when a specificmetal is mentioned as the parent metal, e.g. zirconium, titanium,hafnium, etc., the metal identified should be read with this definitionin mind unless indicated otherwise by the context.

"Parent metal boride" and "parent metal boro compounds" mean a reactionproduct containing boron formed upon reaction between a boron donormaterial, such as boron carbide or boron nitride, and the parent metaland includes a binary compound of boron with the parent metal as well asternary or higher order compounds.

"Parent metal nitride" means a reaction product containing nitrogenformed upon reaction of a nitrogen donor material, such as boronnitride, and the parent metal.

"Parent metal carbide" means a reaction product containing carbon formedupon reaction of a carbon donor material, such as boron carbide, and theparent metal.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view of the setup used to fabricate a plateletreinforced composite body for joining to a steel substrate in accordancewith Example 1;

FIG. 2 is a schematic view of the setup used to carry out the joiningoperation for joining the platelet reinforced composite body fabricatedas shown in FIG. 1 to a steel substrate, in accordance with Example 1;

FIG. 3 is a photograph of the four (4) rectangular bars of plateletreinforced composite material brazed to a carbon steel blade formed inaccordance with Example 1;

FIG. 4 is an approximately 100X magnification photomicrograph of across-section of the brazement between the composite material and carbonsteel backing blade of Example 1;

FIG. 5 is a schematic view of the lay-up used to fabricate the plateletreinforced composite body used in the joining operation of Example 2;

FIG. 6 is a schematic view of the setup employed in the joiningoperation described in Example 2;

FIG. 7 is an approximately 180X magnification photomicrograph of thejoint region between the two platelet reinforced composite bodies ofExample 2;

FIG. 8 is a schematic view of the setup used for carrying out thejoining operation described in Example 3;

FIG. 9 is an approximately 200X magnification photomicrograph of theboundary region between the newly formed platelet reinforced compositematerial and the original platelet reinforced composite body describedin Example 3;

FIG. 10 is a schematic view of the lay-up used to carry out the joiningoperation described in Example 4;

FIG. 11 is a schematic view of a portion of the lay-up used to carry outthe joining operation described in Example 4;

FIG. 12 is an approximately 100X magnification photomicrograph of across-section of the brazement formed in Example 4;

FIG. 13 is a schematic illustration of the setup employed in carryingout the brazing step by induction heating in Example 5;

FIG. 14 is an approximately 100X magnification photomicrograph of thecross-section of the brazement formed in Sample A of Example 5;

FIG. 15 is a schematic illustration of the setup employed in carryingout the brazing operation of Example 6;

FIG. 16 is a schematic view of a portion of the lay-up for the brazingoperation of Example 6;

FIG. 17 is an approximately 100X magnification photomicrograph of across-section of the brazement formed in Example 6;

FIG. 18 is a schematic view of a portion of the lay-up for the brazingoperation of Example 7;

FIG. 19 is an approximately 100X magnification photomicrograph of across-section of the brazement formed in Example 7;

FIG. 20 is an approximately 100X magnification photomicrograph of across-section of the brazement formed in Example 8;

FIG. 21 is a schematic illustration of setup employed in carrying outthe joining operation of Example 10;

FIG. 22 is an approximately 200X magnification photomicrograph of across-section of the joined bodies of Example 10;

FIG. 23 is a schematic illustration of the setup employed in carryingout the joining operation of Example 11;

FIG. 24 is a photograph of the platelet reinforced composite body joinedaccording to the techniques of Example11;

FIG. 25 is a cross-sectional schematic view which shows the relativeorientation of the two bodies which are to be joined in accordance withExample 12;

FIG. 26 is a cross-sectional schematic view of a vertical section of thetwo bodies bonded in accordance with Example 12;

FIGS. 27a and 27b are photographs showing the fillets (weld lines)formed in Embodiments 1 and 2, respectively, of Example 12;

FIG. 28 is a cross-sectional schematic view showing the relativeorientation of two platelet reinforced composite bodies to be joined inaccordance with Example 13;

FIG. 29 is a photograph showing the two platelet reinforced compositebodies bonded in accordance with Example 13;

FIG. 30 is a cross-sectional schematic view of the lay-up used infabricating the platelet reinforced composite bodies of Example 14;

FIG. 31 is a cross-sectional schematic view of the apparatus used injoining the formed platelet reinforced composite bodies in accordancewith Example 14;

FIG. 32 is a photograph of the joined platelet reinforced compositetubes taken immediately after the joining operation of Example 14; and

FIG. 33 is a photograph of the joined tubes after final machining.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention permits one or more bodies to be bonded togetherto form desirable complex structures or shapes or relatively largestructures or shapes without the requirement for any complex steps.

In accordance with a first step of the present invention,self-supporting ceramic bodies are produced by utilizing a parent metal(e.g., zirconium, titanium, and/or hafnium) infiltration and reactionprocess (i.e. reactive infiltration) in the presence of a bed or masscomprising, for example, boron carbide or boron nitride. Such bed ormass is infiltrated by molten parent metal, and the bed may be comprisedentirely of boron carbide, boron nitride, and/or mixtures of boron donormaterials and carbon donor materials and/or nitrogen donor materials.Depending on the particular reactants involved in the reactiveinfiltration, the resulting bodies which are produced comprise one ormore reaction products such as parent metal boron-containing compounds,parent metal carbon-containing compounds, parent metalnitrogen-containing compounds, etc. Alternatively, the mass to beinfiltrated may contain one or more inert fillers admixed therewith toproduce a composite by reactive infiltration, which composite comprisesa matrix of one or more of the aforementioned reaction products and thematrix also may include residual unreacted or unoxidized constituents ofthe parent metal. The filler material may be embedded by the formedmatrix. Regardless of whether a filler material is used, the finalproduct may include a metal (e.g., one or more metallic constituents ofthe parent metal). Still further, in some cases it may be desirable toadd a carbon donor material (i.e., a carbon-containing compound) and/ora boron donor material (i.e., a boron-containing compound) to the bed ormass which is to be infiltrated to modify, for example, the relativeamounts of one formed reaction product to another, thereby modifyingresultant mechanical properties of the composite body. Still further,the reactant concentrations and process conditions may be altered orcontrolled to yield a body containing varying volume percents of ceramiccompounds, metal and/or porosity.

Broadly, in accordance with the first step of the method according tothis invention, the bed or mass which is to be reactively infiltratedmay be placed adjacent to or contacted with a body of molten metal ormetal alloy, which is melted in a substantially inert environment withina particular temperature envelope. The molten metal infiltrates the massand reacts with at least one constituent of the bed or mass to beinfiltrated to form one or more reaction products. At least a portion ofthe formed reaction product is maintained in contact with the metal, andmolten metal is drawn or transported toward the remaining unreacted massby a wicking or capillary action. This transported metal formsadditional reaction product upon contact with the remaining unreactedmass, and the formation or development of a ceramic body is continueduntil the parent metal or remaining unreacted mass has been consumed, oruntil the reaction temperature is altered to be outside the reactiontemperature envelope. The resulting structure comprises, depending uponthe particular materials comprising the bed or mass which is to bereactively infiltrated, one or more of a parent metal boride, a parentmetal boro compound, a parent metal carbide, a parent metal nitride, ametal (which as used herein is intended to include alloys andintermetallics), or voids, or a combination thereof, and these severalphases may or may not be interconnected in one or more dimensions. Thefinal volume fractions of the reaction products and metallic phases, andthe degree of interconnectivity, can be controlled by changing one ormore conditions, such as the initial density of the mass which is to bereactively infiltrated, the relative amounts and chemical composition ofthe materials contained within the mass which is to be reactivelyinfiltrated, the amount of parent metal provided for reaction, thecomposition of the parent metal, the presence and amount of one or morefiller materials, temperature, time, etc.

Typically, the mass to be reactively infiltrated should be at leastsomewhat porous so as to allow for wicking of the parent metal throughthe reaction product. Wicking occurs apparently either because anyvolume change on reaction does not fully close off pores through whichparent metal can continue to wick, or because the reaction productremains permeable to the molten metal due to such factors as surfaceenergy considerations which render at least some of its grain boundariespermeable to the parent metal.

In another aspect of the first step of the invention, a composite isproduced by the transport of molten parent metal into the bed or masswhich is to be reactively infiltrated which has admixed therewith one ormore inert filler materials. In this embodiment, one or more suitablefiller materials are mixed with the bed or mass to be reactivelyinfiltrated. The resulting self-supporting ceramic-metal composite thatis produced typically comprises a dense microstructure which comprises afiller embedded by a matrix comprising at least one parent metalreaction product, and also may include a substantial quantity of metal.Typically, only a small amount of material (e.g., a small amount ofboron carbide) is required to promote the reactive infiltration process.Thus, the resulting matrix can vary in content from one composedprimarily of metallic constituents thereby exhibiting certain propertiescharacteristic of the parent metal; to cases where a high concentrationof reaction product is formed, which dominates the properties of thematrix. The filler may serve to enhance the properties of the composite,lower the raw materials cost of the composite, or moderate the kineticsof the reactions which produce the reaction product and the associatedrate of heat evolution. The precise starting amounts and composition ofmaterials utilized in the reaction infiltration process can be selectedso as to result in a desirable body which is compatible with the secondstep of the invention.

In another aspect of the first step of the present invention, thematerial to be reactively infiltrated is shaped into a preform 35corresponding to the geometry of the desired final composite. Subsequentreactive infiltration of the preform by the molten parent metal resultsin a composite having the net shape or near net shape of the preform,thereby minimizing expensive final machining and finishing operations.Moreover, to assist in reducing the amount of final machining andfinishing operations, a barrier material can at least partially, orsubstantially completely, surround the preform. The use of a graphitematerial (e.g., a graphite mold, a graphite tape product, a graphitecoating, etc.) is particularly useful as a barrier for such parentmetals as zirconium, titanium, or hafnium, when used in combination withpreforms made of, for example, at least one of boron carbide, boronnitride, boron and carbon. Still further, by placing an appropriatenumber of through-holes having a particular size and shape in theaforementioned graphite mold, the amount of porosity which typicallyoccurs within a composite body manufactured according to the first stepof the present invention, can be reduced. Typically, a plurality ofholes is placed in a bottom portion of the mold, or that portion of themold toward which reactive infiltration occurs. The holes function as aventing means which permit the removal of, for example, argon gas whichhas been trapped in the preform as the parent metal reactiveinfiltration front infiltrates the preform.

Still further, the procedures discussed above herein in the Section"Description of Commonly Owned U.S. Patents and Patent Applications" maybe applicable in connection with the first step of the presentinvention.

Once a self-supporting body has been formed in accordance with the firststep of the present invention, the second step of the present inventionis put into effect. The second step of the present invention involves aplurality of different embodiments, each of which is discussed below.

In a first embodiment of the second step of the present invention, atleast one first self-supporting body formed in accordance with the firststep of the invention is contacted with at least one secondself-supporting body formed in accordance with the first step of theinvention, said contacting occurring with or without the application ofexternal pressure upon the contacted bodies. The contacted bodies arethen held together in an appropriate manner (e.g., by the force ofgravity, by some external pressure means, etc.) and are heated to anelevated temperature to permit the bodies to bond together. Stated morespecifically, when at least two bodies made in accordance with the firststep of the present invention are contacted with each other and areheated to a temperature which is above the melting point of at least aportion of the metallic constituent in at least one of the bodies andthe contacted bodies are held at such temperature for an appropriateamount of time and in the presence of, for example, a substantiallyinert atmosphere (e.g., an atmosphere similar to the formationatmosphere utilized in the first step of the present invention), saidcontacted bodies can bond together along at least a portion of the areaof mutual contact and form a well bonded unitary piece. The conditionsutilized to achieve the bond between said at least two contacted bodiescan be tailored so that the original joining area between said at leasttwo bodies is substantially completely indistinguishable from any otherarea in said at least two bodies. For example, if the temperatureutilized to join the bodies is a temperature only slightly above themelting point of at least a portion of the metallic constituent in atleast one of the bodies, the time required for joining may be longerthan the time required for joining when the temperature is significantlyabove the melting point of substantially all of the metallic constituentin both of the bodies.

The choice of particular temperature, atmosphere and time are dependentupon the type of bodies which are to be bonded together as well as thetype of bond which is desired to be formed. For example, if the bodiesto be bonded together comprise substantially the same materials and itis desired that the bond or joining area be substantiallyindistinguishable from any other part of the bodies to be bondedtogether, then a sufficiently high temperature and sufficiently longduration of time needs to be chosen so as to permit such bonding tooccur. Without wishing to be bound by any particular theory orexplanation, it is possible that when the bodies are at a temperatureabove the melting point of at least a portion of the metallicconstituent of at least one of the bodies, then a reaction product ofsimilar composition and size can be formed between the bodies which areto be bonded together. However, if either or both of the temperature ortime is decreased, the tendency for the joining area to bedistinguishable from other portions of the bodies to be joined togetherwill be greater. The precise combination of temperature and time can bechosen by one of ordinary skill in the art by routine experimentation;however, it should be understood that the joining temperature should notexceed a temperature above which shape deformation of any of the bodiesto be joined may occur.

The ability to join said at least two bodies together is a significantachievement because rather than forming a very complex-shaped preform ofa bed or mass which is to be reactively infiltrated or a complex-shapedmold to contain a bed or mass of filler material which is to bereactively infiltrated, a plurality of simpler or less complex shapedpreforms (or molds containing filler material) can be utilized to formself-supporting bodies in accordance with the first step of theinvention. Such formed bodies can thereafter be bonded together to forman intricate or complex-shaped piece or a very large piece. Due to thenature of the joining mechanism, it can be extremely difficult, if notimpossible, to distinguish any joint area from any other area of theformed body. Accordingly, this invention permits the formation ofintricate and complex shapes, as well as large bodies, by combining aplurality of relatively simple shapes made by relatively simpletechniques.

For example, if it was desired to form a "T-shaped" object, it would bepossible to form each portion of the "T" independently by, for example,following the teachings according to the first step of the presentinvention; and thereafter cause each of the separate portions of the "T"to bond together (e.g., by conventional welding or brazing techniques).It is envisioned that a virtually unlimited combination of pieces couldbe joined together to form very complex shapes and/or very large pieces.Accordingly, the ability to form integral bonds between individualpieces is a significant achievement.

In a second embodiment of the second step of the present invention, theplurality of individual bodies which are bonded together do not consistentirely of materials made in accordance with the first step of thepresent invention. For example, materials such as metals, ceramics,etc., can be bonded to articles made in accordance with the first stepof the invention. In this second embodiment of the second step of theinvention, in order for bonding to occur, it can be desirable for sometype of reaction to occur between a body produced in accordance with thefirst step of the invention, and a second body.

In regard to the second embodiment of the second step of the presentinvention, and without wishing to be bound by any particular theory orexplanation, it is possible, in the case of bonding a body made inaccordance with the first step of the invention to a metal body, thatsome type of metallurgical bond may exist between parent metal containedin the body formed in accordance with the first step of the invention,and the metallic body which is bonded thereto. In this instance, sometype of interdiffusion, alloying or formation of desirableintermetallics may occur at the joining area between the bodies to bebonded together. Alternatively, if one of the bodies to be bondedtogether comprises a conventional ceramic, it may be desirable forresidual parent metal in a body formed in accordance with the first stepof this invention to react in some manner (e.g., reduce) with at least aportion of the ceramic body which is to be bonded thereto.

A third embodiment of the second step of the present invention involvesthe placement of materials, similar to those utilized to form theself-supporting body of the first step of the present invention, betweenat least two bodies which are to be bonded together. Specifically, thejoining area which exists between said at least two bodies which are tobe bonded together can be filled with, for example, a powdered parentmetal and a material which is to be reactively infiltrated.Alternatively, the joint can be filled with, for example, a materialwhich is to be reactively infiltrated and a source of parent metal canbe placed into contact with the material which is to be reactivelyinfiltrated. Thus, a reaction is permitted to occur between the parentmetal and the material which is to be reactively infiltrated so as toform a bonding zone at the joining area between the aforementioned atleast two bodies.

In accordance with the third embodiment of the second step of thepresent invention, if the bodies to be joined are of similar composition(e.g., two bodies of the same composition formed in accordance with thefirst step of the present invention), then the processing conditionsutilized to form the joint can be tailored so that the joining area issubstantially indistinguishable from other areas of the aforementionedbodies to be joined. However, if the bodies to be joined have a verydifferent composition, then the joining area will be distinguishable. Itshould be noted that bodies can be substantially different incomposition and can still be joined together by the method of theabove-described third embodiment. For example, a body produced inaccordance with the first step of the present invention can be bondedto, for example, a metal.

It is possible to envision that any number of macrocomposite bodies(i.e., bodies which comprise one or more different materials integrallybonded together) can be produced in accordance with the teachings of thepresent invention. Specifically, bodies made in accordance with thefirst step of the invention could be bonded to bodies of differentcomposition which are also made in accordance with the first step of theinvention; bodies made in accordance with the first step of theinvention could be bonded to other materials such as ceramic materialsor metals; etc. In each of these cases, either material could functionas a substrate for the other material, or as encasement member for theother material, etc.

In a fourth embodiment of the second step of the present invention, anactive brazing material in any suitable form is contacted with thebonding surfaces of two bodies formed in accordance with the first stepof the present invention or, alternatively, the brazing material may beplaced in contact with the bonding surfaces of one body formed inaccordance with the first step of the present invention and a secondbody. Particularly, for example, a foil, rod, plate, paste or powderwhich comprises an active brazing metal or alloy (e.g., an alloycomprising titanium) is placed in contact with at least a portion of thebonding surfaces of at least two self-supporting bodies made inaccordance with the first step of the present invention. Without wishingto be bound by any particular theory or explanation, it appears asthough the active brazing alloy assists in wetting and bonding thematerials together. To achieve bonding by use of an active brazingalloy, the contacted bodies, or at least the bonding surfaces of thecontacted bodies which are in contact with the active brazing alloy, areheated to a temperature which permits the active brazing alloy to bondthe bodies together.

In each of the above-discussed embodiments of the second step of thepresent invention, it may be desirable to bond together bodies made inaccordance with the first step of the invention. In this case, it ispossible that bodies produced in accordance with the first step of thepresent invention may comprise completely different parent metals andthus completely different reaction products. Alternatively, the bodiesmay have been produced by using very similar parent metals and thus thebodies may comprise very similar reaction products. Accordingly, thepresent invention permits bonding to occur between dissimilar materialsdue to the inherent nature of the bond which is formed. Thus, thepresent invention permits the formation of relatively complex shapesand/or relatively large shapes due to the ability to bond similar ordissimilar bodies together in a secure manner.

The following are examples of the present invention. The examples areintended to be illustrative of various aspects of the present invention,however, these examples should not be construed as limiting the scope ofthe invention.

EXAMPLE 1

This Example demonstrates a technique for joining a platelet reinforcedcomposite to a steel. Specifically, a platelet reinforced composite bodywas brazed to a carbon steel using a foil of an active brazing alloy.

The setup used for fabricating the platelet reinforced composite bodiesis shown schematically in FIG. 5.

A platelet reinforced composite body was fabricated by reactivelyinfiltrating zirconium metal into a filler of boron carbide particulate.Specifically, a grade ATJ graphite mold 10 (Union Carbide Company,Carbon Products Division, Cleveland, Ohio) measuring, in its interior,about 4 inches (102 mm) square by about 3 inches (76 mm) tall wasroughened on its inner surfaces with 120 grit silicon carbide abrasivepaper.

The residual graphite dust was blown out of the mold using compressedair. The inside surfaces of the graphite mold 10 were then coated with asingle layer of silicon nitride paint 12 (ZYP SN, ZYP Coatings, Inc.,Oak Ridge, Tenn.). The coated graphite mold 10 was allowed to dry in airfor about 16 hours followed by an approximately one hour drying in aforced air drying oven at a temperature of about 120° C. The coatedgraphite mold 10 was removed from the drying oven and allowed to cool toroom temperature. About 206 grams of 1000 grit TETRABOR® boron carbideparticulate 14 (ESK-Engineered Ceramics, New Canaan, Conn.) having anaverage particle size of about 5 microns was poured into the siliconnitride coated 12 graphite mold 10 and leveled. The graphite mold 10 andits contents were then placed into a tap volume meter (Model 2003 STAV,Stampfvolumeter, J. Engelsmann, A. G., Federal Republic of Germany) andtap loaded about 1000 times to minimize entrapped air and pore space inthe loose bedding of particulate boron carbide 14, thus consolidatingthe powder. About 1250 grams of nuclear grade zirconium sponge 16(Western Zirconium, Ogden, Utah) was placed into the coated graphitemold 10 on top of the tap loaded layer of boron carbide particulate 14to form a lay-up.

The lay-up was placed into a vacuum furnace. The furnace chamber wasevacuated to about 30 inches (762 mm) of mercury vacuum using amechanical roughing pump and backfilled with argon gas. The chamber wasre-evacuated to a working pressure of about 2×10⁻⁴ torr. The furnacetemperature was then increased from substantially room temperature to atemperature of about 1950° C. at a rate of about 240° C. per hour. Uponreaching a temperature of about 1000° C., the furnace was backfilledwith argon gas to a pressure of about 2 psig (14 kPag). An argon gasflow rate of about two liters per minute was established through thefurnace. After maintaining a temperature of about 1950° C. for about twohours, the furnace was then cooled at a rate of about 154° C. per hour.After cooling to a temperature of about 100° C., the furnace was opened,and the lay-up was removed and disassembled to reveal a plateletreinforced composite body comprising zirconium diboride, zirconiumcarbide, and some residual zirconium alloy.

The setup used to carry out the joining operation is shown schematicallyin FIG. 2.

Four (4) right rectangular pieces of the formed platelet reinforcedcomposite material 20, each comprising by weight about 5.0% zirconium,56.0% zirconium diboride, and about 39.0% zirconium carbide and eachmeasuring about 1.281 inches (32.5 mm) in length, by about 0.266 inch(6.7 mm) in width, and by about 0.246 inch (6.2 mm) in height wereelectro-discharge machined from the formed platelet reinforced compositematerial and then surface ground to their final dimensions. The residuefrom the grinding and machining process was removed using a series ofsilicon carbide abrasive papers, namely 60 grit, 120 grit, and 180 grit.The four (4) platelet reinforced composite samples, or coupons 20, wererinsed in acetone and then ultrasonically cleaned in acetone for about 5minutes. The steel body 22 to be joined to the platelet reinforcedcomposite material was prepared for joining by first flat grinding thesurfaces to be joined, smoothing the ground surfaces with 60 grit, 120grit, and 180 grit silicon carbide abrasive paper, and finally, cleaningoff the grinding and sanding residues with acetone. The final acetonetreatment comprised an approximately 5 minute soak in acetone in anultrasonic bath. The ultrasonically cleaned steel body 22 was allowed toair dry.

Four (4) Cusin ABA-1 brazing alloy foils 24 (GTE, Wesgo ProductsDivision, Belmont, Calif.) were cut slightly larger than the 1.281inches (32.5 mm) by 0.266 inch (6.7 mm) area to be joined. Each brazingalloy foil 24 weighed between 0.11 and 0.14 grams. Each foil 24 wasplaced between the platelet reinforced composite material 20 and thesteel substrate 22 and the bodies to be bonded were held in place with agraphite fixture 26. The steel substrate 22 was supported by a graphitedish 28 measuring about 10 inches (254 mm) square and about 1 inch (25mm) deep. About 200 grams of titanium sponge 30 (Teledyne Wah ChangAlbany, Albany Oreg.) and about 50 grams of nuclear grade zirconiumsponge 32 (Western Zirconium, Ogden, Utah) were placed at opposite endsof the graphite dish 28 to complete the lay-up.

The lay-up was placed into a vacuum furnace at about room temperature.The furnace chamber was evacuated to about 30 inches (762 mm) of mercuryvacuum and backfilled with argon gas. The furnace chamber was evacuateda second time to a working pressure of about 2×10⁻⁴ torr. The furnacetemperature was then increased to about 750° C. at a rate of about 400°C. per hour. After maintaining a temperature of about 750° C. for aboutone hour, the furnace chamber was backfilled with argon gas to apressure of about 2 psig (14 kPag). An argon gas flow rate of about twoliters per minute was established. The furnace temperature was thenincreased to about 850° C. at a rate of about 250° C. per hour. Aftermaintaining a temperature of about 850° C. for about 15 minutes, thefurnace temperature was decreased at a rate of about 350° C. per hour.After the furnace had cooled to substantially room temperature, thefurnace was opened and the lay-up was removed. Inspection of the steelbody 22 and platelet reinforced composite 20 assembly revealed that thefour (4) rectangular bars of platelet reinforced composite material 20were joined to the steel body 22. A photograph of the brazed assembly isshown in FIG. 3.

One (1) of the four (4) brazed platelet reinforced composite bars wassectioned, mounted, and polished for optical microscopy. Anapproximately 100X magnification photomicrograph of the cross-section ofthe brazed region is shown in FIG. 4. The photomicrograph shows thatgood bonding was achieved between the composite material and the steelsubstrate.

Shear strength measurements were carried out to measure the strength ofthe bond formed between the platelet reinforced composite material andthe steel to which it was brazed. Specifically, the brazed assembly wasmounted in a steel jig on the base of a Sintec Model CITS-2000/6universal testing machine (System Integration Technology, Inc.,Stoughton, Mass.). The assembly was oriented such that the bond area layin a vertical plane and that the direction of the applied force wassubstantially transverse to the radial direction of the assembly (i.e.,at a right angle to an imaginary line joining the center of the bondregion to the center of the steel piece). The load was applied with ananvil of square cross-section attached to a load cell having a capacityof about 5,000 lbs. which in turn was attached to the cross-head of theuniversal testing machine. A compliant layer comprising several sheetsof copper foil each measuring about 15 mils thick was placed between themoveable anvil and the brazed assembly. The anvil was brought down at aconstant speed of about 0.51 millimeters per minute against the brazedassembly until the rectangular bar of platelet reinforced compositematerial failed as a result of the shear stresses set-up as a result ofthe applied shear load. The shear stress-caused failure was calculatedby dividing the bond area into the maximum applied load.

A total of three (3) rectangular bars of brazed platelet reinforcedcomposite material were shear tested by the technique described above.The measured shear strengths ranged from about 6,800 psi (47 MPa) toabout 9700 psi (67 MPa).

In conclusion, this Example demonstrates a process for brazing aplatelet reinforced composite body to a carbon steel substrate. Atechnique for measuring the strength of the brazement was described.Three measurements of the strength of the brazement were performed.

EXAMPLE 2

This Example demonstrates that through application of heat and pressurealone (i.e., without the incorporation of any kind of filler or brazingmaterial between the bodies) two bodies of platelet reinforced compositematerial can be joined to one another. The set-up used to accomplish thejoining operation is shown schematically in cross-section in FIG. 6. Thelay-up used to fabricate the platelet reinforced composite bodies to bejoined to one another is shown schematically in FIG. 5.

About 300 grams of methylene chloride was placed into a 1/2 gallon (1.9liter) NALGENE® plastic jar (Nalge Company, Rochester, N.Y.). About 2.0grams of XUS 40303.00 experimental binder (Dow Chemical Company,Midland, Mich.) was dissolved into the methylene chloride solvent toform a binder solution. About 200 grams of 1,000 grit TETRABOR® boroncarbide particulate was then stirred into the binder solution in theplastic jar to form a slurry.

As shown in FIG. 5, a grade AGSX graphite mold 52 (Union CarbideCorporation, Carbon Product Division, Danbury, Conn.) measuring about2.0 inches (50 mm) square and about 2.25 inches (55 mm) deep, asmeasured in its interior, was soaked for about one hour in methylenechloride to saturate the graphite with the solvent. After the soakingoperation, some of the boron carbide slurry was sediment cast into thesoaked graphite mold 52. Specifically, a sediment cast preform 50 wasfabricated by pouring the slurry into the mold and allowing the boroncarbide particulate to settle out of the slurry and form a dense packedbed. The bulk residual binder solution was daubbed off of the topsurface of the sediment cast preform 50 in the graphite mold 52. Thegraphite mold 52 and its sediment cast preform 50 contained within wasthen placed into a drying box at room temperature to remove the residualmethylene chloride solvent in a slow and controlled manner to avoidrupturing the sediment cast preform 50 of boron carbide. After drying inthe drying box for about 24 hours, virtually all of the methylenechloride had been removed. The mass of the sediment cast preform 50 wasfound to be about 41.6 grams and its thickness about 0.8 inch (20 mm).

The graphite mold 52 and its dried sediment cast preform 50 containedwithin was then placed into the chamber of a resistance heatedcontrolled atmosphere furnace. The furnace chamber was evacuated toabout 30 inches (762 mm) of mercury vacuum and back-filled with argongas a total of three times to purge the furnace chamber of any residualair. An argon gas flow rate of about two liters per minute through thefurnace at an over pressure of about 1 psi (7 kPa) was established. Thefurnace temperature was then raised from approximately room temperatureto a temperature of about 300° C. at a rate of about 108° C. per hour.The temperature was then increased from about 300° C. to about 400° C.at a rate of about 10° C. per hour. The temperature was then increasedfrom about 400° C. to about 600° C. at a rate of about 67° C. per hour.After maintaining a temperature of about 600° C, for about four hours,substantially all of the ceramic binder had been removed from thesediment cast preform. Accordingly, the furnace temperature wasdecreased to substantially room temperature at a rate of about 300° C.per hour. After cooling to substantially room temperature, the graphitemold 52 containing the sediment cast preform 50 was removed from thefurnace.

About 297 grams of zirconium sponge 54 (Consolidated Astronautics SaddleBrook, N.J.) was placed into the graphite mold 52 over the sediment castpreform 50 of boron carbide and levelled to form a lay-up. The lay-upwas placed into a resistance heated controlled atmosphere furnace. Thefurnace was evacuated to about 30 inches (762 mm) of mercury vacuum andthen back-filled with argon gas. An argon gas flow rate of about twoliters per minute through the furnace at an over pressure of about 2 psi(14 kPa) was established. The furnace temperature was then increasedfrom about room temperature to about 1900° C. at a rate of about 375° C.per hour. After maintaining a temperature of about 1900° C. for abouttwo hours, the furnace temperature was decreased at a rate of about 375°C. per hour. When the furnace temperature had reached substantially roomtemperature, the lay-up was removed from the furnace. The contents ofthe graphite mold 52 were removed from the mold to reveal that thezirconium metal 54 had infiltrated and reacted with the sediment castboron carbide preform 50 to produce a platelet reinforced composite bodycomprising zirconium diboride, zirconium carbide, and some residualmetal.

A section of the formed platelet reinforced composite body was madeusing electro-discharge machining. The machined section was mounted in athermoplastic polymer material and polished with diamond polishing pastefor subsequent examination in the optical microscope. Quantitative imageanalysis of an optical image of the polished section of the plateletreinforced composite body revealed the presence of about 7.7 volumepercent residual metal in the composite.

Test coupons 60 of the platelet reinforced composite body wereelectro-discharge machined from the 2.0 inch (51 mm) square plateletreinforced composite body described above. Each coupon 60 measured about0.645 inch (16.4 mm) in length by about 0.19 inch (4.8 mm) thick. One ofthe coupons 60 measured about 0.4 inch (10 mm) in width while the othermeasured about 0.45 inch (11.4 mm) in width. As shown in FIG. 6, thetest coupons 60 were oriented within the graphite jig 62 in such a waythat the side or face of each coupon 60 having the largest area wascontacted with the other coupon 60. The orientation was such that thelong dimension of each coupon 60 was at an approximate right angle tothat of the other coupon 60. The area of contact or overlap amounted toabout 0.25 square inch (164 square mm).

The graphite jig 62 and the test coupons 60 to be joined to one anotherwere placed into a resistance heated controlled atmosphere furnace.About 200 grams of zirconium sponge 64 (Consolidated Astronautics,Saddle Brook, N.J.) were placed into a graphite dish 66 which in turnwas also placed into the chamber of the controlled atmosphere furnace toserve as a gettering agent for any residual oxygen or nitrogen impurityin the furnace. A mass of about 2.2 kilograms 68 was suspended from theend of the lever arm such that the applied pressure on the plateletreinforced composite test coupons 60 amounted to about 150 psi (1.0MPa). The furnace chamber was evacuated to about 30 inches (762 mm)mercury vacuum and then back-filled with argon gas. An argon gas flowrate of about two liters per minute was established through the furnacechamber at an over pressure of about 2 psi (14 kPa). The furnacetemperature was then increased from about room temperature to atemperature of about 1800° C. at a rate of about 400° C. per hour. Aftermaintaining a temperature of about 1800° C. for about 1/2 hour, thefurnace temperature was decreased at a rate of about 350° C. per hour.After the furnace temperature had decreased to substantially roomtemperature, the graphite jig 62 and its test coupons 60 to be joined toone another were removed from the furnace and inspected. The two (2)platelet reinforced composite test coupons 60 could not be separatedfrom one another using hand pressure.

The joined platelet reinforced composite test coupons 60 were sectionedusing electro-discharge machining. The cut section was then mounted andpolished with diamond paste for subsequent examination in the opticalmicroscope. An approximately 180X magnification photomicrograph of thejoint region is shown in FIG. 7. No evidence of a former boundarybetween the coupons 60 is visible, suggesting mutual penetration ofzirconium diboride and zirconium carbide from each test coupon into theother.

This Example therefore illustrates a technique for joining two plateletreinforced composite bodies to one another by heating said bodies to asemi-liquid state and contacting the surfaces of the bodies under amodest pressure. Quality bonds were formed in short periods of timeunder relatively low pressures.

EXAMPLE 3

This Example demonstrates that one platelet reinforced composite bodycan be joined to another by forming a thin platelet reinforced compositelayer at the interface. The set up for carrying out such a joining meansis illustrated schematically in FIG. 8.

A platelet reinforced composite body measuring about 2.0 inches (51 mm)square by about 0.73 inch (18.5 mm) thick was made by substantially thesame techniques as the platelet reinforced composite made in Example 2.The sediment cast boron carbide particulate preform, after firing in anargon atmosphere to remove the ceramic binder, weighed about 58.6 grams.The bulk density of the boron carbide preform was calculated to be about1.22 grams per cubic centimeter or about 48.4% of theoretical density.

About 430.5 grams of zirconium sponge (Consolidated AstronauticsDivision of United-Guardian, Inc., Hauppauge, N.Y.) was placed into thegraphite mold over the fired boron carbide preform and levelled to forma lay-up. The lay-up was placed into a resistance heated controlledatmosphere furnace and exposed to substantially the same atmosphere andtemperature as the lay-up in Example 2. A platelet reinforced compositebody was recovered from the graphite molds after the furnace had cooledto substantially room temperature. The platelet reinforced compositecomprised zirconium diboride, zirconium carbide, and some residualmetal.

Two (2) test coupons 80 each measuring about 0.75 inch (19 mm) long byabout 0.33 inch (8.4 mm) wide by about 0.125 inch (3.2 mm) thick weremachined from the previously described composite using electro-dischargemachining. The test coupons 80 were sand blasted and then cleanedultrasonically in an acetone bath, then allowed to air dry. The testcoupons weighed about 3.1 grams each.

A brazing filler material 82 comprising particulates of a parent metaland a solid oxidant was prepared. Specifically, about 67.1 grams ofzirconium particulate (-325 mesh, Atlantic Equipment Engineers,Burgenfield, N.J.), having substantially all particles smaller thanabout 45 microns in diameter, about 1.1 grams of ELMERS® ProfessionalCarpenter's Wood Glue (Borden Company, Columbus, Ohio), about 5 grams of1,000 grit TETRABOR® boron carbide particulate (Exolon-ESK Company,Tonawanda, N.Y.) and about 48.1 grams of distilled water were combinedin a one liter NALGENE® plastic jar (Nalge Company, Rochester, N.Y.) toform a slurry 82. A quantity of this slurry was brushed onto the largestbase on each of the test coupons, and the test coupons were cementedtogether with the slurry. After the slurry 82 had dried, the mass of theassembly was measured and the quantity of dried particulates and glue,which had been applied between the faces, amounted to about 0.35 grams.

The test coupons 80 which were loosely cemented together with the driedslurry admixture 82 were placed into a graphite boat 84 and fixed inplace with a weight 86 on top of the test coupon assembly 80,82.Specifically, the weight 86 anchoring the test coupon assembly 80 inplace comprised a portion of platelet reinforced composite tilemeasuring about 2.0 inches (51 mm) long by about 1.0 inch (25 mm) wideby about 0.75 inch (19 mm) thick. About 200 grams of zirconium sponge 88(Consolidated Astronautics Division of United-Guardian, Inc., Hauppauge,N.Y.) was poured into a graphite crucible 90 measuring 2.0 inches (51mm) square by about 3.0 inches (76 mm) deep. The graphite crucible 90and its contents of zirconium sponge 88 were placed into the graphiteboat 84 to serve as a getter for oxygen and nitrogen impurities. Agraphite lid 92 was placed on top of the graphite boat 84, but no effortwas made to seal the lid to the boat. About 200 grams of additionalzirconium sponge 94 (Consolidated Astronautics, New Canaan, Conn.) werepoured evenly over the top surface of the graphite lid 92 to serve asadditional gettering material for gaseous impurities. The graphite boat84 and its contents were placed into a resistance heated controlledatmosphere furnace. The furnace chamber was evacuated to about 30 inches(762 mm) of mercury vacuum and back-filled with argon gas. An argon gasflow rate of about two liters per minute was established through thefurnace at an over pressure of about 2 psi (14 kPa). The furnacetemperature was increased from about room temperature to a temperatureof about 1900° C. at a rate of about 400° C. per hour. After maintaininga temperature of about 1900° C. for about 10 minutes, the temperaturewas decreased at a rate of about 350° C. per hour. After cooling tosubstantially room temperature, the graphite boat 84 and its contentswere removed from the furnace and disassembled. The platelet reinforcedcomposite test coupons 80 were found to have bonded to one another. Thefillet or bond line between the test coupons appeared wedge shaped,perhaps due to uneven loading during the furnace run. A section of thebond region was removed from the side of the assembly where the testcoupons 80 were closest to one another using electro-dischargemachining. An approximately 320X magnification optical photomicrographof the mounted and polished cross-section of the bond region is shown inFIG. 9. The photomicrograph reveals that the joint region, like theplatelet reinforced composite test coupons, comprises zirconium diboride100, zirconium carbide 62, and some residual metal 104. The size of themicrostructural features, however, appears smaller than thosecorresponding features in either of the original platelet reinforcedcomposite test coupons.

EXAMPLE 4

This Example demonstrates a further embodiment of the technique ofjoining a platelet-reinforced composite body to a steel substrate by abrazing operation. The setup employed in carrying out the fabrication ofthe platelet-reinforced composite body is substantially the same as thatshown in FIG. 5. The setup employed in carrying out the brazingoperation is shown schematically in FIGS. 10 and 11.

A platelet-reinforced composite was fabricated by reactivelyinfiltrating zirconium metal into a filler of boron carbide particulate,as described herein.

As shown in FIG. 5, a Grade ATJ graphite crucible 52 (Union CarbideCompany, Carbon Products Division, Cleveland, Ohio) measuring about 3.0inches (76 mm) square in its interior by about 3.25 inches (83 mm) tallwas roughened on its inner-surfaces with approximately 120 grit siliconcarbide abrasive paper. The residual graphite dust was blown out of thecrucible using compressed air.

About 0.46 grams of XUS 40303.00 Experimental Binder (Midland, Mich.)was placed into an approximately 8 ounce (0.24 liter) NALGENE® plasticjar (Nalge Company, Rochester, N.Y.) along with about 77.2 grams ofisopropyl alcohol. The plastic jar was sealed, and the jar and itscontents were placed onto an EBERBACH® paint shaker (EberbachCorporation, Ann Arbor, Mich.) and shaken for about 11/2 hours tocompletely dissolve the binder into the isopropyl alcohol. The plasticjar and its contents were then removed from the paint shaker, and about91.15 grams of 1000 grit TETRABOR® boron carbide particulate (ESKEngineered Ceramics, New Canaan, Conn.) having an average particle sizeof about 5 microns was added to the contents of the jar. The plastic jarand its contents were then returned to the EBERBACH® shaker and shakenfor about two hours to thoroughly mix the boron carbide particulate withthe binder solution. The plastic jar and its contents were then removedfrom the shaker, and the slurry of boron carbide and binder solution wassediment cast by pouring the slurry into the graphite crucible andallowing the boron carbide particulate to settle out. The graphitecrucible 52 and its contents were then placed into an evaporatingchamber to remove the isopropyl alcohol in a controlled manner. Afterdrying the sediment cast preform 50 in the evaporating chamber for about16 hours, the isopropyl alcohol had evaporated to the point where nonewas visible on top of the sediment casting. The door to the evaporatingchamber was opened slightly and the evaporating/drying operation wascontinued for about an additional two hours. The graphite crucible 52and the sediment cast preform 50 contained within the crucible wereremoved from the evaporation chamber and placed into a drying oven.After further drying at a temperature of about 45° C. for about onehour, the graphite crucible and its contents were transferred to asecond drying oven at a temperature of about 70° C. After drying at atemperature of about 70° C. for about one hour, virtually all of theisopropyl alcohol had been removed from the sediment cast boron carbidepreform 50.

The graphite crucible 52 and its contents were then placed into a vacuumfurnace. The vacuum chamber was evacuated to a vacuum of about 30.0inches (762 mm) of mercury and backfilled with argon gas. Afterrepeating this evacuation and backfilling procedure, an argon gas flowrate of about two liters per minute through the vacuum chamber wasestablished. The furnace temperature was then increased from about roomtemperature to a temperature of about 200° C. at a rate of about 100° C.per hour. At a temperature of about 200° C., the temperature was thenincreased to about 350° C. at a rate of about 20° C. per hour. At atemperature of about 350° C., the temperature was then increased toabout 670° C. at a rate of about 107° C. per hour. After maintaining atemperature of about 670° C. for about two hours, the furnacetemperature was then decreased at a rate of about 80° C. per hour. Atabout room temperature, the furnace was opened and the graphite crucible52 and its contents were removed. The sediment cast boron carbidepreform 50 contained within the graphite crucible 52 was found to have amass of about 89.2 grams and dimensions of about 3.04 inches (77 mm)square by about 0.49 inch (12 mm) thick. A green density of about 1.21grams per cubic centimeter or about 48% of the theoretical density ofboron carbide was thereby computed. The change in mass upon firing in anargon atmosphere to a temperature of about 670° C. indicated that thebinder had been removed by this operation.

About 595.8 grams of nuclear grade zirconium sponge 54 (WesternZirconium Company, Ogden, Utah) was poured into the graphite crucible 52on top of the sediment cast boron carbide preform 50 and levelled toform a lay-up. The lay-up was placed into the vacuum chamber of a vacuumfurnace. The vacuum chamber was evacuated to a vacuum of about 30.0inches (762 mm) of mercury using a mechanical roughing pump and thenbackfilled with argon gas. The vacuum chamber was pumped out again usingthe roughing pump. After achieving about 30.0 inches (762 mm) of mercuryvacuum, a high vacuum source was connected to the vacuum chamber and thechamber was evacuated further to a final working pressure of about1.2×10⁻⁵ torr. The furnace temperature was then increased from aboutroom temperature to a temperature of about 1950° C. at a rate of about240° C. per hour. After reaching a temperature of about 1000° C., thehigh vacuum source was isolated from the vacuum chamber, and the chamberwas backfilled with argon gas. An argon gas flow rate of about twoliters per minute through the chamber at an over pressure of about 2 psi(14 kPa) was established. After maintaining a temperature of about 1950°C. for about two hours, the furnace temperature was decreased to atemperature of about 1500° C. at a rate of about 90° C. per hour. At atemperature of about 1500° C., the furnace temperature was then furtherdecreased at a rate of about 300° C. per hour. When the furnacetemperature had reached about room temperature, the lay-up was removedfrom the furnace. The contents of the graphite crucible 52 were removedfrom the crucible to reveal that the zirconium metal 54 had infiltratedand reacted with the sediment cast boron carbide preform 50 to produce aplatelet-reinforced composite comprising zirconium diboride, zirconiumcarbide, and some residual metal.

Referring to FIGS. 10 and 11, four (4) right rectangular bars 20 ofplatelet-reinforced composite material were electro-discharge machinedfrom the formed platelet-reinforced composite and then surface ground tofinal dimensions of about 1.281 inches (32.5 mm) long by about 0.266inch (6.7 mm) wide by about 0.246 inch (6.2 mm) high. The residue fromthe grinding and machining operations was removed using 60 grit, 120grit, and 180 grit, respectively, silicon carbide abrasive papers. Thefour (4) rectangular bars 20 were then rinsed in acetone andultrasonically cleaned in acetone for about five minutes.

The steel body 22 to be joined to the platelet-reinforced composite bars20 (hereafter referred to as a "backing plate") was of substantially thesame size, shape, and chemical composition as the steel body 22described in Example 1. Specifically, the steel backing plate 22comprised by weight about 0.38-0.43% C, about 0.60-0.80% Mn, ≦0.040% P,≦0.040% S, about 0.20-0.35% Si, about 1.65-2.00% Ni, about 0.20-0.30%Mo, and the balance Fe (nominally American Iron and Steel InstituteAlloy No. 4640). This steel backing plate 22 was prepared for joining byfirst flat grinding the surfaces to be joined, smoothing the groundsurfaces with 60 grit, 120 grit, and 180 grit silicon carbide abrasivepaper, respectively, and cleaning off the grinding and sanding residueswith acetone. The final cleansing treatment comprised an approximatelyfive minute soak in acetone in an ultrasonic bath. The ultrasonicallycleaned steel backing plate 22 and platelet-reinforced composite bars 20were allowed to air dry.

Eight (8) Cusin-ABA-1 brazing alloy foils 24 (GTE, Wesgo ProductsDivision, Belmont, Calif.) were cut slightly larger than the about 1.281inches (32.5 mm) by about 0.266 inch (6.7 mm) area to be joined. Eachbrazing alloy foil 24 weighed between about 0.11-0.12 grams. A gradeOFHC copper foil 25 (Lucas-Milhaupt, Cudahy, Wisc.) measuring about0.005 inch (0.13 mm) thick and having substantially the same length andwidth dimensions as the brazing alloy foils 24 described above wasplaced between a pair of the brazing alloy foils 24 and orientedsimilarly (see FIG. 11). Each of the four (4) foil assemblies was thenplaced between a rectangular bar 20 and a steel backing plate 22. Eachassembly, comprising foil assembly 24 and 25, the rectangular bars 20and the steel backing plate 22, was held in place with a graphitefixture 26 as shown in FIG. 10. The steel backing plate 22 was supportedby a graphite dish 28 measuring about 10.0 inches (254 mm) square byabout 1.0 inch (25 mm) deep. About 200 grams of titanium sponge 30(Teledyne Wah Chang Albany, Albany, Oreg.) and about 50 grams of nucleargrade zirconium sponge 32 (Western Zirconium, Ogden, Utah) were placedat opposite ends of the graphite dish 28 to complete the setup.

The setup was placed into a vacuum furnace at about room temperature.The vacuum chamber was evacuated to about 30.0 inches (762 mm) ofmercury vacuum using a mechanical roughing pump and backfilled withargon gas. The vacuum chamber was evacuated a second time to a vacuum ofabout 30.0 inches (762 mm) of mercury with the roughing pump, afterwhich a source of high-vacuum was connected to the vacuum chamber topump said chamber down to a final working pressure of about 2×10⁻⁴ torr.The furnace temperature was then increased to about 850° C. at a rate ofabout 900° C. per hour. Upon reaching a temperature of about 750° C.,the high-vacuum source was isolated from the vacuum chamber and thechamber was backfilled with argon gas to a pressure of about 2 psig (14kPag). An argon gas flow rate of about two liters per minute was thenestablished through the chamber and maintained for the balance of thefurnace run. After holding at a temperature of about 850° C. for about15 minutes, the furnace temperature was decreased to about 800° C. at arate of about 300° C. per hour. At a temperature of about 800° C., thefurnace temperature was then decreased to about 400° C. at a rate ofabout 120° C. per hour. At a temperature of about 400° C., the furnacetemperature was then decreased at a rate of about 300° C. per hour.After the furnace had cooled to about room temperature, the furnace wasopened and the lay-up was removed. Inspection of the steel andplatelet-reinforced composite assembly revealed that the four (4)rectangular bars 20 were joined to the steel backing plate 22. Thebrazed assembly looked substantially the same as the assembly shown inFIG. 3.

One (1) of the four (4) brazing junctions between theplatelet-reinforced composite and the steel backing plate was sectioned,mounted, and polished for examination in an optical microscope. Anapproximately 100X magnification photomicrograph of the cross-section ofthe brazed region is illustrated in FIG. 12, showing intimate contactbetween the platelet-reinforced composite material 20, the three (3)foils 24, 25, and the steel substrate 22.

Shear strength measurements were carried out on the brazed assembly insubstantially the same manner as described in Example 1. The averageshear stress of three tests was about 9220 psi (64 MPa) with a standarddeviation of about 158 psi (1.1 MPa).

This Example thus demonstrates another embodiment of a process forbrazing a platelet-reinforced composite body to a carbon steelsubstrate.

EXAMPLE 5

This Example demonstrates the use of induction heating to join aplatelet-reinforced composite body to a steel substrate by a brazingoperation. The setup used to accomplish the brazing operation is shownschematically in FIG. 13.

A platelet-reinforced composite body was fabricated by substantially thesame technique as was employed in fabricating the body described inExample 2, as illustrated in FIG. 5.

Four (4) right rectangular prisms 20 of the platelet-reinforcedcomposite body were electro-discharge machined from theplatelet-reinforced composite material and then surface ground to afinal dimension of about 0.39 inch (10 mm) square by about 1/8 inch (3mm) in height. The residue from the grinding and machining processes wasremoved using, 60 grit, 120 grit, and 180 grit, respectively, siliconcarbide abrasive paper. One (1) of the two (2) square faces of each ofthe platelet-reinforced composite prisms 20 was polished usingprogressively finer diamond polishing-compound, with the finest, i.e.,the last polish in the series, having diamond particles averaging about1.0 micron in size. The platelet-reinforced composite prisms 20 werethen rinsed in acetone followed by an ultrasonic cleaning treatment inacetone for about five minutes.

A carbon steel substrate 102 measuring about 21/2 inches (63 mm) long byabout 1.0 inch (25 mm) wide by about 1/8 inch (3 mm) thick was preparedfor brazing to the rectangular prisms 20 by flat grinding theapproximately 21/2 inch (63 mm) by about 1.0 inch (25 mm) face,smoothing the ground surface with 60, 120, and 180, respectively, gritsilicon carbide abrasive paper, and finally polishing the surface to bebrazed to the platelet-reinforced composite prisms 20 with approximately1200 FEPA (600 grit) silicon carbide abrasive paper. The residues fromgrinding, sanding, and polishing were removed by first rinsing the steelsubstrate in an acetone bath, then giving the steel substrate anapproximately five minute ultrasonic cleansing treatment in an acetonebath. After cleaning, the rectangular prisms 20 and the steel substrate102 were allowed to dry in air.

The following Samples describe various lay-ups used to join arectangular prism 20 to a carbon steel substrate 102.

Sample A

A Cusin-1-ABA brazing alloy foil 24 (GTE Wesgo Division, Belmont,Calif.) measuring about 0.39 inch (10 mm) square by about 0.002 inch(0.05 mm) thick was placed flat onto the carbon steel substrate 102. One(1) rectangular prism 20 was then placed on top of the brazing alloyfoil 24 such that its polished face completely contacted the brazingalloy foil 24 to form a lay-up.

Sample B

The lay-up of Sample B was substantially the same as the lay-up ofSample A, except that the orientation of the rectangular prism 20 wassuch that the un-polished square face contacted the Cusin-1-ABA brazingalloy foil 24.

Sample C

The lay-up of Sample C was substantially the same as the lay-up forSample A, except that two (2) Cusin-1-ABA brazing alloy foils 24 wereplaced between the rectangular prism 20 and the carbon steel substrate102.

Sample D

The lay-up of Sample D was substantially the same as the lay-up ofSample C, except that the orientation of the rectangular prism 20 wassuch that the un-polished square face contacted the two (2) Cusin-1-ABAbrazing alloy foils 24.

The setup comprising the carbon steel substrate 102 and the brazingalloy foils 24 with the rectangular prisms 20 of Samples A-D mountedthereon was placed onto a support plate 104 in an inductively heatedcontrolled atmosphere furnace. The furnace chamber was first evacuatedto a vacuum of about 30.0 inches (762 mm) of mercury using a mechanicalroughing pump and then backfilled with argon gas to about atmosphericpressure. An argon gas flow rate of about 0.5 liter per minute wasestablished through the furnace. The furnace temperature was thenincreased from about room temperature to a temperature of about 1000° C.at a rate of about 70° C. per minute; After maintaining a temperature ofabout 1000° C. for about five minutes, the furnace temperature wasdecreased at a rate of about 30° C. per minute. After the sample hadcooled to about room temperature, the furnace chamber was opened and thecarbon steel substrate 102 and the lay-ups assembled thereon wereremoved. Visual inspection showed that all of the rectangular prisms 20were bonded to the carbon steel substrate 102. The Sample A lay-up wassectioned, mounted, and polished with diamond paste for examination ofthe bonded region in an optical microscope. An approximately 100Xmagnification photomicrograph of a cross-section of the bonded region isshown in FIG. 14. The photomicrograph shows that the region between theplatelet-reinforced composite material 20 and the steel substrate 102 issubstantially completely filled with brazing alloy 24, suggesting thatthe brazing alloy foil material 24 bonded to the surface 106 of therectangular prism 20, and to the surface 108 of the steel substrate 102,thus joining the two (2) materials to one another.

This Example therefore demonstrates that a platelet-reinforced compositebody can be joined to a carbon steel body by means of a brazingoperation employing induction heating.

EXAMPLE 6

This Example demonstrates the use of a protective zirconium foil pouchor envelope to help maintain an inert, non-oxidizing atmosphere aroundthe brazing lay-up. The setup used to accomplish the brazing operationis shown schematically in cross-section in FIG. 15.

A platelet-reinforced composite body was fabricated by substantially thesame technique as was employed in fabricating the body described inExample 2.

A section of the formed platelet-reinforced composite body was cut usingelectro-discharge machining. The machined section was mounted in plasticand polished with progressively finer diamond polishing pastes inpreparation for examination using an optical microscope. The finest(last) polish contained diamond particles averaging about 1.0 micron insize. This polished sample was placed into a Model 500 PSEM scanningelectron microscope (Philips, N.V., Eindhoven, The Netherlands) and ten(10) backscattered electron images were photographed. These photographswere then placed on a light table and video images of each photographwere obtained by viewing through a DAGE-MTI Series 68 video camera(DAGE-MTI, Inc., Michigan City, Ind.). The video signal was sent to aModel DV-4400 Scientific Optical Analysis System (Lamont Scientific ofState College, Pa.) and then stored. Specific color and gray levelintensity ranges were assigned to specific microstructural features(platelets, ceramic matrix, metal, pores). To verify that the colorassignments were accurate, a comparison was made between a video imagewith assignments and the original black and white image. Ifdiscrepancies were noted, corrections were made to the video imageassignments with a Model 2200/2210 39C2 hand held digitizing pen anddigitizing board (Numonics Corporation, Lansdale, Pa.). Representativevideo images with assignments were analyzed automatically by thecomputer software contained in the Lamont Scientific Optical AnalysisSystem to-give area percent platelets, area percent ceramic matrix, areapercent metal, and area percent porosity, which are substantially thesame as volume percents. Quantitative image analysis using theaforementioned technique revealed that the platelet-reinforced compositebody contained about five volume percent of residual metal.

A right rectangular bar 20 was electro-discharge machined from the sameplatelet-reinforced composite material discussed above and then surfaceground to a final dimension of about 1.0 inch (25 mm) in length, byabout 1/4 inch (6 mm) in width, by about 1/4 inch (6 mm) in height. Theresidue from the grinding and machining process was removed using 60grit, 120 grit, and 180 grit, respectively, silicon carbide abrasivepaper. The surface of the rectangular bar 20 to be brazed to a steelsample 102 was polished using progressively finer diamond polishingcompounds, with the finest (last) in the series having diamond particlesaveraging about 1.0 micron in size. The rectangular bar 20 was thenrinsed in acetone and then ultrasonically cleaned for approximately fiveminutes in an acetone bath.

Two (2) carbon steel test coupons 102 each measuring about 21/2 inches(63 mm) long, by about 1.0 inch (25 mm) wide, by about 1/8 inch (3 mm)thick, were prepared for brazing to the platelet-reinforced compositetest bar by flat grinding the surfaces to be joined, smoothing theground surfaces with 60, 120, and 180 grit, respectively, siliconcarbide abrasive paper, and-finally polishing the surface to be brazedto the platelet-reinforced composite body with approximately 1200 FEPA(600 grit) silicon carbide abrasive paper. The residues from grinding,sanding, and polishing were removed by first rinsing the test coupons inan acetone bath and then treating the carbon steel test coupons forapproximately five minutes in an ultrasonically agitated acetone bath.After cleaning, both the rectangular bar 20 and the carbon steel testcoupons 102 were allowed to dry in air.

A Cusin-1-ABA brazing alloy foil 24 (GTE Wesgo Division, Belmont,Calif.) measuring about 0.24 inch (6 mm) square by about 0.002 inch(0.050 mm) thick was placed near one end of each of the two (2) carbonsteel test coupons 102, as shown in FIG. 16. The rectangular bar 20 wasplaced over the ends of the carbon steel test coupons 102 such that thebrazing foils 24 were substantially completely covered, thus forming alay-up for brazing.

The lay-up of FIG. 16, comprising the rectangular bar 20, the two (2)carbon steel test coupons 102, and the two (2) Cusin-1-ABA brazing foils24, was placed between two layers of zirconium foil (PhoenixMetallurgical Corporation, Houston, Tex.), each layer comprising twosheets of zirconium foil measuring about 4.0 inches (102 mm) long byabout 2.0 inches (51 mm) wide by about 0.0002 inch (0.050 mm) thick. Asshown in FIG. 15, a pouch 110 was fabricated by hand folding andcrimping the edges of the two (2) zirconium foil layers together to forma seam. The formed seam was not air-tight. The zirconium foil pouch 110was used to isolate the lay-up from residual oxidizing gases in thefurnace atmosphere by gettering any such gases. The zirconium foil pouch110 and its contents were then placed into a Grade ATJ graphite boat 112(Union Carbide Company, Carbon Products Division, Cleveland, Ohio)measuring about 6 inches (152 mm) square, by about 4.0 inches (102 mm)tall and having a loose fitting graphite lid 114 to cover the open endof the boat 112. About 100 grams of nuclear grade zirconium sponge 32(Western Zirconium, Ogden, Utah) were placed at opposite ends of thegraphite boat 112 to assist in keeping the local environment within thegraphite boat 112 free of oxidizing gas contaminants.

The graphite boat 112 and its contents were placed into a vacuum furnaceat about room temperature. The vacuum chamber was evacuated to a vacuumof about 30 inches (762 mm) of mercury using a mechanical roughing pumpand then backfilled with argon gas. After pumping down the vacuumchamber a second time to a vacuum of about 30 inches (762 mm) ofmercury, a high vacuum source was connected to the vacuum chamber andthe chamber was pumped down to a final working pressure of less thanabout 2×10⁻⁴ torr. The furnace temperature was then increased to about750° C. at a rate of about 400° C. per hour. After maintaining atemperature of about 750° C. for about one hour, the source of highvacuum was isolated from the vacuum chamber and the vacuum chamber wasbackfilled with argon gas. An argon gas flow rate of about 0.5 litersper minute at an overpressure of about 2 psi (14 kPa) through the vacuumchamber was established. The remainder of the run was conducted underthis flowing argon gas atmosphere. The furnace temperature was thenincreased from about 750° C. to about 850° C. at a rate of about 250° C.per hour. A temperature of about 850° C. was held for about 15 minutes,then the furnace temperature was decreased at a rate of about 350° C.per hour. After the furnace had cooled to about room temperature, thefurnace was opened and the graphite boat 112 and its contents wereremoved from the vacuum chamber. The zirconium foil pouch 110 and itscontents were removed from the graphite boat 112 and disassembled. Itwas determined that the carbon steel test coupons 102 had bonded to therectangular bar 20.

One of the bonded regions was sectioned, mounted, and diamond polishedfor examination in the optical microscope. An approximately 100Xmagnification photomicrograph of the cross-section of the bonded regionis shown in FIG. 17. The photograph indicates that bonding was achievedbetween the rectangular bar 20 and the carbon steel test coupon 102 viaa brazing process because the region between the two is substantiallycompletely filled with the Cusin-1-ABA brazing alloy foil material 24(GTE Wesgo Division, Belmont, Calif.). The brazing alloy foil material24 thus appears to have melted, wet the two (2) surfaces of theplatelet-reinforced composite bar 20 and the carbon steel test coupon102, expelled the void space, and adhered to the two (2) surfaces toform a brazement.

EXAMPLE 7

This Example demonstrates a further embodiment of the process forjoining a platelet-reinforced composite body to la steel body by abrazing operation. The setup used to carry out the brazing operation issubstantially the same as that shown in FIG. 15.

A platelet-reinforced composite body was fabricated by substantially thesame techniques as was employed in fabricating the platelet-reinforcedbody described in Example 2. A right rectangular bar 20 waselectro-discharge machined from this platelet-reinforced composite bodyand then surface ground to a final dimension of about 1.0 inch (25 mm)in length, by about 1/4 inch (6 mm) in width, by about 1/4 inch (6 mm)in height. One of the approximately 1.0 inch (25 mm) by about 1/4 inch(6 mm) faces was polished using a series of incrementally finer diamondpolishing pastes, with the last paste in the series having diamondparticles averaging about 1 micron in size. The rectangular bar 20 wasthen rinsed in acetone and cleaned ultrasonically in an acetone bath forabout five minutes. Once face of the rectangular bar 20 was thenadditionally polished with approximately 1200 grit silicon carbideabrasive paper.

Two (2) carbon steel test coupons 102, each measuring about 21/2 inches(63 mm) long, by about 1.0 inch (25 mm) wide, by about 1/8 inch (3 mm)thick, were prepared for brazing to the platelet-reinforced compositebar 20 by flat grinding the surfaces to be joined, smoothing the groundsurfaces by abrading with 60 grit, 120 grit, and 180 grit, respectively,silicon carbide abrasive paper. The debris from grinding and sanding wasremoved by first rinsing the carbon steel test coupons 102 in an acetonebath and then giving the test coupons 102 an ultrasonic cleaningtreatment in acetone for about five minutes. After drying the cleanedsteel test coupons 102 in air, the two (2) faces to be brazed werepolished with approximately 1200 grit silicon carbide abrasive paper.

The two (2) carbon steel test coupons 102 were arranged polished side upas shown in FIG. 18. About 0.09 grams of LUCANEX™ 721 brazing alloyfiller material 116 (Lucas-Milhaupt, Inc., Cudahy, Wisc.) having theconsistency of paste was placed onto each of the steel coupons 102 inthe vicinity of the desired brazement. The rectangular bar 20 was thenplaced across the two (2) carbon steel test coupons 102 and so orientedsuch that its polished face contacted the brazing alloy filler material116 on the carbon steel test coupons 102. The platelet-reinforcedcomposite bar was pressed down onto the steel test coupons 102 tosqueeze out excess brazing alloy filler material 116 from the joint. Theexcess brazing alloy filler material 116 was left on the steel testcoupons 102. Thus, a lay-up for brazing was formed.

Similar to the lay-up for Example 6, shown in FIG. 15, a zirconium foilcontainer 110 was fabricated around the lay-up for brazing. Thezirconium foil container 110 was perforated at several locations alongthe sides to assist in maintaining the shape integrity of the foilcontainer 110 during the various evacuation and backfilling operations.The zirconium foil container 110 was then placed inside a Grade ATJgraphite boat 112 (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio) measuring about 6.0 inches (152 mm) square by about 4.0inches (102 mm) tall. About 100 grams of nuclear grade zirconium sponge32 (Western Zirconium, Ogden, Utah) were placed at opposite ends of thegraphite boat 112 to assist in keeping the local environment within thegraphite boat 112 free of oxidizing gas contaminants. A loose fittingGrade ATJ graphite lid 114 (Union Carbide Corporation, Carbon ProductsDivision, Cleveland, Ohio) was placed over the open end of the graphiteboat 112.

The graphite boat 112 and its contents were placed into the vacuumchamber of a vacuum furnace at about room temperature. The vacuumchamber was evacuated to a vacuum of about 30.0 inches (762 mm) ofmercury using a mechanical roughing pump and then backfilled with argongas to about atmospheric pressure. After pumping down the vacuum chambera second time to a vacuum of about 30.0 inches (762 mm) of mercury withthe roughing pump, a high vacuum source was connected to the vacuumchamber and the chamber was pumped down further to a final operatingpressure of less than about 2×10⁻⁴ torr. The furnace temperature wasthen increased to a temperature of about 750° C. at a rate of about 400°C. per hour. After maintaining a temperature of about 750° C. for aboutone hour, the high vacuum source was isolated from the vacuum chamberand the chamber was backfilled with argon gas to an overpressure ofabout 2 psi (14 kPa). An argon gas flow rate of about 0.5 liters perminute was established through the chamber. The remainder of the run wasconducted under this flowing argon gas atmosphere. The furnacetemperature was then increased from about 750° C. to about 912° C. at arate of about 250° C. per hour. After maintaining a temperature of about912° C. for about 15 minutes, the temperature was then decreased at arate of about 350° C. per hour. After the furnace had cooled to aboutroom temperature, the furnace was opened and the graphite boat 112 andits contents were removed from the vacuum chamber. The zirconium foilcontainer 110 was disassembled and the lay-up was removed to reveal thatthe rectangular bar 20 had bonded to the two (2) carbon steel testcoupons 102.

One (1) of the two (2) brazed regions was sectioned, mounted, anddiamond polished for examination in the optical microscope. Anapproximately 100X magnification photomicrograph of the cross-section ofthis brazed region is shown in FIG. 19. The photomicrograph indicatesthat bonding was achieved between the rectangular bar 20 and the carbonsteel test coupon 102 with the brazing material 116.

Thus, a further embodiment of the process for joining aplatelet-reinforced composite body to a steel body by a brazingoperation was demonstrated.

EXAMPLE 8

This Example demonstrates yet another embodiment of the process forjoining a platelet-reinforced composite body to a carbon steel body bymeans of a brazing operation.

A platelet-reinforced composite body was fabricated by substantially thesame method as was described in Example 1. The lay-up used in carryingout the fabrication of the platelet-reinforced composite body wassubstantially the same as that illustrated in FIG. 1.

The lay-up employed in joining the platelet-reinforced composite bars 20to the steel backing plate 22 was substantially the same as thatdescribed in Example 1 and illustrated in FIG. 2. The differences in thebrazing operation between the present Example and that of Example 1 aredescribed herein.

Specifically, four (4) platelet-reinforced composite bars 20 weremachined, ground, polished, and cleaned in substantially the same manneras were the bars discussed in Examples 1 and 4. Similarly, the steelbacking plate 22 to be joined to the platelet-reinforced composite bars20 was ground and cleaned in substantially the same manner as was thesteel backing plate described in Examples 1 and 4. This steel backingplate 22 was also of substantially the same composition as the steelbacking plate in Examples 1 and 4 steel backing plates, comprising byweight about 0.38-0.43% C, about 0.60-0.80% Mn, ≦0.040% P, ≦0.040% S,about 0.20-0.75% Si, about 1.65-2.00% Ni, about 0.20-0.30% Mo, and thebalance Fe (nominally American Iron and Steel Institute Alloy No. 4640).

The lay-up for brazing was placed into the vacuum chamber of a vacuumfurnace at about room temperature. The vacuum chamber was evacuated to avacuum of about 30.0 inches (762 mm) of mercury using a mechanicalroughing pump and then backfilled with argon gas to about atmosphericpressure. The vacuum chamber was then evacuated a second time using theroughing pump to a vacuum of about 30.0 inches (762 mm) of mercury, atwhich point a source of high vacuum was connected to the vacuum chamberand the chamber was evacuated to a final operating pressure of less thanabout 2×10⁻⁴ torr. The furnace temperature was then increased to about750° C. at a rate of about 400° C. per hour. After maintaining atemperature of about 750° C. for about one hour, the furnace temperaturewas increased to a temperature of about 900° C. at a rate of about 250°C. per hour. A temperature of about 900° C. was maintained for about 15minutes, and the temperature was decreased at a rate of about 350° C.per hour. After the furnace had cooled to about room temperature, thevacuum chamber pressure was increased to atmospheric pressure, thefurnace was opened, and the lay-up was removed from the vacuum chamber.Inspection of the lay-up revealed that the four (4) reinforced compositebars 20 were joined to the steel backing plate 22.

One (1) of the four (4) brazed platelet-reinforced composite bars wassectioned through the brazement and that section was mounted andpolished for examination in the optical microscope. An approximately100X magnification photomicrograph of the cross-section of a regionbetween the platelet-reinforced composite material 20 and the steelbacking plate 22 where the bonding appeared to be continuous is shown inFIG. 20. This particular cross-section shows that the region between theplatelet-reinforced composite material 20 and the steel 22 issubstantially completely filled with the brazing alloy filler material116.

EXAMPLE 9

This Example demonstrates yet another embodiment of the technique ofjoining a platelet-reinforced composite body to a carbon steel body bymeans of a brazing operation. The fabrication of the platelet-reinforcedcomposite bars was substantially the same as that described in Example 1and as illustrated in FIG. 5. The procedures employed in machining,grinding, polishing, and cleaning the platelet-reinforced composite barswas substantially the same as those described in Examples 1 and 4. Thepreparation of the steel backing plate for brazing was alsosubstantially the same as that described in Examples 1 and 4. Theprocedure employed in brazing the platelet-reinforced composite bars tothe steel backing plate was similar to that described in Example 4 andas illustrated in FIG. 10 with the following differences describedherein.

The lay-up was placed into the vacuum chamber of a vacuum furnace atabout room temperature. The vacuum chamber was evacuated to a vacuum ofabout 30.0 inches (762 mm) of mercury by means of a mechanical roughingpump. The chamber was then backfilled with argon gas to aboutatmospheric pressure. The vacuum chamber was evacuated a second time bymeans of the roughing pump to a vacuum of about 30.0 inches (762 mm) ofmercury and was then connected to a source of high vacuum to evacuatethe vacuum chamber to a final working pressure of less than about 2×10⁻⁴tort. The furnace temperature was then increased to a temperature ofabout 500° C. at a rate of about 250° C. per hour. At a temperature ofabout 500° C., the source of high vacuum was isolated from the vacuumchamber and the chamber was backfilled with argon gas to an overpressureof about 2 psi (14 kPa). An argon gas flow rate of about two liters perminute through the vacuum chamber was established. The remainder of thebrazing operation was conducted under this flowing argon gas atmosphere.The furnace was then increased from about 500° C. to a temperature ofabout 850° C. at a rate of about 500° C. per hour. After maintaining atemperature of about 850° C. for about 15 minutes, the furnacetemperature was then decreased to a temperature of about 800° C. at arate of about 300° C. per hour. At a temperature of about 800° C., thefurnace temperature was then further decreased to a temperature of about400° C. at a rate of about 120° C. per hour. At a temperature of about400° C., the furnace temperature was then further decreased at a rate ofabout 300° C. per hour. When the furnace had cooled to about roomtemperature, the vacuum chamber was opened and the lay-up was removed.Inspection of the steel and platelet-reinforced composite assemblyrevealed that the four (4) rectangular bars of the platelet-reinforcedcomposite material were joined to the steel backing plate.

To set a lower bound on the strength of the joints between theplatelet-reinforced composite bars and the steel backing plate, a prooftest was conducted. Specifically, the proof test comprised applying acompressive shear load to the joint in substantially the same manner aswas described in Example 1. Instead of loading the joint to failure,however, the joint was loaded up to a force corresponding to a shearstress of about 2000 psi (13.8 MPa). As soon as the proof stress ofabout 2000 psi (13.8 MPa) was reached, the load was immediately removed.Each of the other three (3) joints was similarly tested. The brazedassembly maintained its structural and dimensional integrity.

This Example thus demonstrates yet another embodiment of a process forjoining a platelet-reinforced composite body to a steel body by means ofa brazing operation. Additionally, a proof test of the brazements isdescribed.

EXAMPLE 10

In a manner similar to Example 2, this Example presents a furtherembodiment of the concept of joining two (2) platelet-reinforcedcomposite bodies through application of heat and pressure, wherein theplatelet-reinforced composite bodies contain a relatively low amount ofresidual metal. The setup used to accomplish the joining operation isshown in FIG. 21. The lay-up used to fabricate the platelet-reinforcedcomposite bodies to be joined to one another is substantially the sameas that shown in FIG. 5.

A platelet-reinforced composite body was fabricated in substantially thesame manner as the platelet-reinforced composite body fabricated inExample 2, with three exceptions. First, the graphite mold 52 comprisedGrade ATJ graphite (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio) and measured about 3.0 inches (76 mm) square and about31/2 inches (89 mm) deep as measured in its interior. Second, afterdrying and firing, the mass of the sediment cast preform 50 was found tobe about 134 grams and its thickness about 0.75 inch (19 mm). The bulkdensity of the sediment cast preform 50 was determined to be about 1.21grams per cubic centimeter or about 48% of the theoretical density ofboron carbide. Third, about 854 grams of zirconium sponge 54(Consolidated Astronautics, Saddlebrook, N.J.) was placed into the GradeATJ mold 52 (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio) over the sediment cast boron carbide preform 50 andlevelled to form a lay-up.

After heating the lay-up in substantially the same manner as wasdescribed in Example 2, the lay-up was removed from the furnace and thecontents of the graphite mold 52 were removed from the mold to revealthat the zirconium metal 54 had infiltrated and reacted with thesediment cast boron carbide preform 50 to produce a platelet-reinforcedcomposite body comprising zirconium diboride, zirconium carbide, andsome residual metal.

A representative polished sample of the formed platelet-reinforcedcomposite body was prepared in substantially the same manner as wasdescribed in Example 2. Quantitative image analysis on the polishedsample was performed in substantially the same manner as was describedin Example 6, revealing the presence of about 3.4 volume percentresidual metal in the platelet-reinforced composite.

Test coupons 60 of the platelet-reinforced composite body wereelectro-discharge machined from the 3.0 inches (76 mm) squareplatelet-reinforced composite body described above. Each coupon 60measured about 0.75 inch (19 mm) long by about 0.336 inch (8.5 mm) wideby about 0.124 inch (3.1 mm) thick. The machined test coupons 60 wereoriented in such a way that the approximately 0.75 inch (19 mm) by about0.336 inch (8.5 mm) face of each test coupon 60 was contacted with thatof the other coupon 60. The orientation was such that the long dimensionof each coupon 60 was at an approximate right angle to that of the othercoupon 60. The area of contact amounted to about 0.11 square inch (73square mm).

The crossed test coupons were placed into the graphite jig 118, as shownin FIG. 21. The graphite jig 118 comprised a Grade ATJ graphite base 120(Union Carbide Corporation, Carbon Products Division, Cleveland, Ohio),a Grade ATJ graphite pedestal 122 (Union Carbide Corporation, Cleveland,Ohio), graphite bolts 124 (Poco Graphite, Inc., Decatur, Tex.), graphitenuts 126 (Poco Graphite, Inc., Decatur, Tex.), and a Grade DFP-1graphite crosshead 128 (Poco Graphite, Inc., Decatur, Tex.). Thegraphite jig 118 and the test coupons 60 to be joined to one anotherwere then placed into the vacuum chamber of a vacuum furnace. Thegraphite nuts 126 at each end of the graphite crosshead 128 weretightened until the loading on the test coupons amounted to about 16.9pounds (75 Newtons) which converted to a normal stress of about 150 psi(1.04 MPa). The vacuum chamber was sealed and then evacuated to a vacuumof about 30.0 inches (762 mm) of mercury and then backfilled with argongas. An argon gas flow rate of about two liters per minute wasestablished through the vacuum chamber at an overpressure of about 2 psi(14 kPa). The furnace temperature was then increased from about roomtemperature to a temperature of about 1800° C. at a rate of about 400°C. per hour. After maintaining a temperature of about 1800° C. for aboutone half hour, the furnace temperature was decreased at a rate of about350° C. per hour. After the furnace temperature had decreased tosubstantially room temperature, the graphite jig 118 and test coupons 60mounted within the jig were removed from the furnace. The two (2)platelet-reinforced composite test coupons 60 were removed from thegraphite jig 118 and inspected. The two (2) test coupons 60 could not beseparated from one another using hand pressure.

The joined platelet-reinforced composite test coupons 60 were sectionedusing electro-discharge machining. The cut section was then mounted andpolished with diamond paste for examination in a Model 500 PSEM scanningelectron microscope (Philips, N.V., Eindhoven, The Netherlands)employing backscattered electron imaging. An approximately 200Xmagnification photomicrograph of the joint region is shown in FIG. 22.As in the case of the joint region shown in FIG. 7, the joint regionshown in FIG. 22 (marked by the X's) similarly shows that the formerboundary between the coupons 60, is substantially indistinguishable.

This Example therefore illustrates that platelet-reinforced compositebodies containing residual metal can be joined to one another by heatingthe bodies and contacting the surfaces of the bodies under pressure.

EXAMPLE 11

This Example demonstrates yet another embodiment of the technique forjoining two (2) platelet-reinforced composite to one another by heatingthe bodies and contacting the surfaces under a slight pressure. Thesetup used for carrying out this bonding is shown schematically in FIG.23.

About 300 grams of methylene chloride were placed into an approximately11/2 gallon (1.9 liter) plastic jug. About 2.0 grams of XUS 40303.00Experimental Binder (Dow Chemical Company, Midland, Mich.) was dissolvedinto the methylene chloride to form a binder solution. About 200 gramsof 1000 grit TETRABOR® boron carbide particulate (ESK EngineeredCeramics, New Canaan, Conn.) having an average particle size of about 5microns was then stirred into the binder solution in the plastic jar toform a slurry. The slurry was roll-mixed for about 11/2 hours tothoroughly disperse the slurry constituents.

Referring to FIG. 5, a Grade AGSX graphite mold 52 (Union CarbideCorporation, Carbon Products Division, Cleveland, Ohio) measuring about3.0 inches (76 mm) square by about 31/2 inches (89 mm) tall in itsinterior was soaked for about one hour in methylene chloride to saturatethe graphite with the solvent. After the soaking operation, some of theboron carbide slurry was sediment cast into the soaked graphite mold 52.Specifically, a sediment cast preform 50 was fabricated by pouring theslurry into the mold 52 and allowing the boron carbide particulate tosettle out of the slurry and form a dense packed bed. During thesedimentation process, the graphite mold 52 and its contents were placedinto a vacuum chamber which was evacuated to a vacuum of between 20.0and 30.0 inches (508 and 762 mm) of mercury using a mechanical roughingpump, in order to minimize the amount of trapped air in the sediment.The bulk residual binder solution was removed by blotting off excessliquid from the top surface of the sediment cast preform 50 in thegraphite mold 52. The graphite mold 52 containing the sediment castpreform 50 was then placed into the tapping chamber of a Model 2003 STAVStampfvolumeter tap volume meter (J. Englesmann, A.G., Federal Republicof Germany) and tapped about 150 times to further consolidate the boroncarbide particles. The graphite mold 52 containing the sediment castpreform 50 was then placed into a drying box at room temperature toremove the residual methylene chloride solvent in a slow and controlledmanner so as to avoid rupturing the sediment cast preform 50. Afterdrying in a drying box for about 24 hours, the graphite mold 52containing the sediment cast preform 50 was transferred to a drying ovenat a temperature of about 125° C. After drying at a temperature of about125° C. for about 16 hours, the graphite crucible and its contents wasthen placed back into the tap volume meter and tapped about 150 moretimes.

The graphite mold 52 and the sediment cast preform 50 were fired toremove substantially all of the binder from the preform 50.Specifically, the graphite mold 52 containing the dried sediment castpreform 50 was then placed into the vacuum chamber of a furnace. Thefurnace chamber was evacuated to a vacuum of about 30.0 inches (762 mm)of mercury and backfilled with argon gas. An argon gas flow rate ofabout two liters per minute through the vacuum chamber at anoverpressure of about 2 psi (14 kPa) was established. The furnacetemperature was then raised from about room temperature to a temperatureof about 200° C. at a rate of about 100° C. per hour. The temperaturewas then increased from about 200° C. to about 350° C. at a rate ofabout 20° C. per hour. The temperature was then increased from about350° C. to about 600° C. at a rate of about 50° C. per hour. Uponreaching a temperature of about 600° C., power to the heating elementsof the furnace was interrupted and the furnace was allowed to cool to atemperature of about 50° C. At a temperature of about 50° C., thegraphite mold 52 and its sediment cast preform 50 contained within wasremoved from the furnace. The sediment cast preform 50 was determined tohave a mass of about 279 grams and dimensions of about 3.0 inches (76mm) square by about 13/4 inches (45 mm) thick. The bulk density of thesediment cast boron carbide preform 50 was calculated to be about 1.07grams per cubic centimeter or about 42.5% of the theoretical density ofboron carbide.

About 1889 grams of nuclear grade zirconium sponge 54 (WesternZirconium, Ogden, Utah) was placed into the graphite mold 52 over thesediment cast preform 50 of boron carbide particulate and levelled toform a lay-up. The formed lay-up was placed back into the vacuum chamberof the vacuum furnace. The chamber was sealed, evacuated to a vacuum ofabout 30.0 inches (762 mm) of mercury using a mechanical roughing pump,and then backfilled with argon gas. After evacuating the vacuum chambera second time to a vacuum of about 30.0 inches (762 mm) of mercury usingthe roughing pump, power to the heating elements was applied and thefurnace temperature was increased from about room temperature to atemperature of about 1900° C. at a rate of about 238° C. per hour. Uponreaching a temperature of about 1000° C., the vacuum chamber wasbackfilled with argon gas. An argon gas flow rate through the vacuumchamber of about two liters per minute at an overpressure of about 2 psi(14 kPa) was established. The remainder of the furnace run was conductedunder this flowing argon gas atmosphere. After maintaining a temperatureof about 1900° C. for about two hours, the furnace temperature wasdecreased at a rate of about 238° C. per hour. When the furnacetemperature had reached about room temperature, the vacuum chamberpressure was reduced to atmospheric pressure and the lay-up was removedfrom the vacuum chamber. The contents of the graphite mold 52 wereremoved from the mold to reveal that the zirconium metal 54 hadinfiltrated and reacted with at least a portion of the sediment castboron carbide preform 50 to produce a platelet-reinforced composite bodycomprising zirconium diboride, zirconium carbide, and some residualmetal. An approximately 0.45 inch (11 mm) thick layer of particulateboron carbide preform material 50 located substantially at the bottom ofthe preform relative to the zirconium metal 54 remained uninfiltrated.

A section of the formed platelet-reinforced composite body was removedusing electro-discharge machining. The machined section was mounted inplastic and polished with diamond polishing paste for subsequentexamination in the optical microscope. Quantitative image analysis ofseveral polished sections, as described in detail in Example 4, revealedthe presence of about 34 volume percent residual metal in the composite.

Two (2) shaped coupons were also electro-discharge machined from theformed platelet-reinforced composite body and are shown in cross-sectionin FIG. 23. Specifically, one (1) shaped coupon 129 was in the form of adisc, measuring about 0.985 inch (25 mm) in diameter by about 0.125 inch(3 mm) thick, while the other shaped coupon 131 substantially resembledan anvil measuring about 1/2 inch (13 mm) in diameter by about 1.0 inch(25 mm) in overall height. The electro-discharge machined coupons werecleaned in an acetone bath.

The machined and cleaned test coupons 129 and 131 were placed into thejig 130 illustrated in FIG. 23. Specifically, the graphite jig 130illustrated in FIG. 23 comprised a Grade ATJ graphite base and verticalsection 132 (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio), a graphite cantilever beam 134 (Poco Graphite, Inc.,Decatur, Tex.), graphite fulcrum pins 136 (Poco Graphite, Inc., Decatur,Tex.), a mass 138 comprising a platelet reinforced composite body, agraphite means 140 (Poco Graphite, Inc., Decatur, Tex.) for connectingsaid mass 138 to said cantilever beam 134, and a Grade ATJ graphiteplaten 142 (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio). A mass 138 of about 2.2 kilograms was suspended fromthe end of the cantilever beam 134 component of the jig 130 to produce acompressive stress of about 150 psi (1.04 MPa) over the 1/2 inch (13 mm)diameter of the anvil shaped coupon body 131. The compressive stressnear the tip of the coupon 31 was, of course, much greater; therefore,the applied stress of about 150 psi (1.04 MPa) represented the minimumapplied compressive stress.

The jig 130 and its contained test pieces was then placed into thevacuum chamber of a vacuum furnace. About 100 grams each of zirconiumsponge 32 (Western Zirconium, Ogden, Utah) and hafnium sponge 144(Teledyne Wah Chang Albany, Albany, Oreg.) were distributed evenlyaround the base 132 of the jig 130 to serve as gaseous "getters" toassist in maintaining an essentially non-reactive atmosphere in thevacuum chamber during the furnace run. The vacuum chamber was sealed andevacuated to a vacuum of about 30.0 inches (762 mm) of mercury and thenbackfilled with argon gas. After re-evacuating the vacuum chamber asecond time using the mechanical roughing pump, a high vacuum source wasconnected to said vacuum chamber to further evacuate said chamber to afinal operating pressure of less than about 2×10⁻⁴ torr. The furnacetemperature was then increased from about room temperature to atemperature of about 1800° C. at a rate of about 400° C. per hour. At atemperature of about 1000° C., the high vacuum source was isolated fromthe vacuum chamber and the chamber vacuum was maintained for theduration of the furnace run using only the mechanical roughing pump asthe vacuum source. After maintaining a temperature of about 1800° C. forabout one half hour, the furnace temperature was decreased at a rate ofabout 350° C. per hour. After the furnace temperature had decreased toabout room temperature, the vacuum chamber pressure was increased toatmospheric pressure and the jig 130 and its contents were removed fromthe vacuum chamber and machined to remove tarnish and burrs. As shown inFIG. 24, the heat and applied pressure had the effect of bonding theplatelet reinforced composite bodies into a single mass. The formerboundary between the bodies could be distinguished visually.

This Example illustrates that platelet reinforced composite bodiescontaining residual metal can be joined to one another by heating saidbodies and contacting the surfaces of the bodies under a modestpressure.

EXAMPLE 12

This Example demonstrates the joining of a platelet-reinforced compositebody to a titanium alloy. FIG. 10 is a cross-sectional schematic view ofthe relative orientation of the platelet-reinforced composite body andthe sheet of titanium alloy employed in the joining operation. Thelay-up employed in fabricating the platelet-reinforced composite bodywas substantially the same as that depicted in FIG. 5. The fabricationof the platelet reinforced composite body is herein described.

A preform was fabricated by sediment casting a slurry comprising boroncarbide particulate, methyl ethyl ketone and a binder agent.Specifically, about 0.25 grams of XUS 40303.00 Experimental Binder (DowChemical Co., Midland, Mich.) was added to about 115 cubic centimetersof methyl ethyl ketone contained within a NALGENE® plastic bottle (NalgeCo., Rochester, N.Y.) having a volume of about 1 liter. The plasticbottle and its contents were placed into an EBERBACH® shaker (EberbachCorp., Ann Arbor, Mich.) and shaken for approximately 1 hour to dissolvethe binder into the methyl ethyl ketone solvent. After forming thisbinder solution, the plastic bottle was opened and about 100 grams of1000 grit TETRABOR® boron carbide particulate (ESK Engineered Ceramics,Distributed by Wacker Chemicals Inc., New Canaan, Conn.) having anaverage particle diameter of about 5 microns was added to the bindersolution in the plastic bottle along with about 3 or 4 BURUNDUM® ballmilling stones (U.S. Stoneware Corp., Mahwah, N.J.) each measuring about1/2 inch (13 mm) in diameter by about 1/2 inch (13 mm) high. TheNALGENE® plastic jar was resealed and placed back onto the EBERBACH™shaker and shaken again for approximately 2 hours to thoroughly dispersethe particles of boron carbide in the binder solution.

The slurry of boron carbide and binder solution was immediately pouredinto a Grade ATJ graphite crucible (Union Carbide Co., Carbon ProductsDivision, Cleveland, Ohio) whose interior measured about 3 inches (76mm) square by about 3.25 inches (83 mm) high. The slurry was poured intothe crucible at a slight angle to avoid trapping air in the slurry.

The graphite crucible and the slurry contained within were placed into avented drying chamber contained within a fume hood and covered with alayer of construction paper to reduce somewhat the rate of evaporationof solvent from the sediment of boron carbide and binder solution. Thebulk of the methyl ethyl ketone solvent evaporated overnight (about16-24 hours) while the crucible and its contents sat in the dryingchamber at about room temperature. The graphite crucible and thesediment cast preform contained within were then transferred to a dryingoven. After drying for approximately 1 hour at a temperature of about45° C. in air at atmospheric pressure, the graphite crucible and itscontents were transferred to a second drying oven at a temperature ofabout 70° C. After drying at approximately 70° C. for about 2 hours, thegraphite crucible and its contents were removed from the drying oven andweighed. The sediment cast preform weighed about 95.6 grams and measuredabout 3 inches (76 mm) square by about 0.51 inches (13 mm) thick.

The graphite crucible and its contents were then fired at an elevatedtemperature to remove the organic binder from the sediment cast boroncarbide preform. Specifically, the graphite crucible and its contentswere placed into a resistance heated retort at about room temperature.The retort chamber was evacuated to about 30 inches (762 mm) of mercuryvacuum and then backfilled with argon gas to about atmospheric pressure.After repeating the evacuation and backfilling procedure, an argon gasflow rate of about 2 standard liters per minute through the retortchamber was established. The retort and its contents were then heatedfrom about room temperature to a temperature of about 200° C. at a rateof about 100° C. per hour. Upon reaching a temperature of about 200° C.,the temperature was then increased to about 350° C. at a rate of about20° C. per hour. Upon reaching a temperature of about 350° C., thetemperature was then increased to a temperature of about 670° C. at arate of about 64° C. per hour. Upon reaching a temperature of about 670°C., the temperature was then decreased to about room temperature at arate of about 80° C. per hour. Once the retort had cooled tosubstantially room temperature, the graphite crucible and the sedimentcast boron carbide preform contained within were removed from the retortchamber. The weight of the preform was found to be about 95.2 grams. Apreform bulk density of about 1.34 grams per cubic centimeter wascalculated, which corresponded to about 53% of the theoretical densityof boron carbide.

About 573 grams of nuclear grade zirconium sponge (Western Zirconium,Ogden, Utah) was then placed into the graphite crucible on top of theboron carbide preform to form a lay-up. The lay-up comprising thegraphite crucible and its contents was then placed into a retort atsubstantially room temperature. The retort chamber was evacuated toabout 30 inches (762 mm) of mercury vacuum and then backfilled withargon gas to substantially atmospheric pressure. The retort chamber wasevacuated a second time to a reduced pressure of about 2.0×10⁻⁴ torr.The temperature of the retort and its contents was then increased fromabout room temperature to a temperature of about 1950° C. at a rate ofabout 192° C. per hour. From about room temperature to a temperature ofabout 1000° C., the retort chamber was heated under vacuum. At atemperature of about 1000° C., the retort was backfilled withcommercially pure argon gas to a pressure of about 2 psig (14 kPag). Anargon gas flow rate of about 2 standard liters per minute through theretort chamber was established. During the switch from vacuum to argongas atmospheres, the furnace heating rate was not interrupted. Theremainder of the run was carried out under this argon gas atmosphere.After maintaining a temperature of about 1950° C. for about 2 hours, thetemperature was then decreased to about 1400° C. at a rate of about 75°C. per hour. Upon reaching a temperature of about 1400° C., the rate ofcooling of the retort and its contents was increased such that atemperature approximately equal to room temperature was reached in about4 hours. After the retort and its contents had cooled to approximatelyroom temperature, the retort chamber was opened and the lay-up wasremoved from the retort and disassembled. A platelet reinforcedcomposite body comprising zirconium diboride, zirconium carbide andabout 6 volume percent residual unreacted parent metal (as determined byquantitative image analysis) was recovered.

A block measuring about 1 inch (25 mm) square by about 0.25 inch (6 mm)thick was sliced out of the recovered composite body usingelectro-discharge machining (EDM). After removing residual EDM debris bysandblasting, the block had a surface finish of about 24-70 microinchesR_(a) (0.6-1.8 microns R_(a)).

Referring to FIG. 25, the machined composite body 200 was contactedagainst a titanium alloy sheet 202 comprising by weight about 6%aluminum, 4% vanadium and the balance titanium and measuring about 2inches (51 mm) long by about 1 inch (25 mm) wide by about 0.042 inch(1.07 mm) thick to form an assembly 208 to be joined. One side of thecomposite body 200 was aligned with the width dimension of the titaniumalloy sheet 202.

Two joining embodiments are described in this Example. The first joiningembodiment, along seam 204, is described below. The second embodiment,performed along seam 210 and described in a subsequent paragraph, wasperformed shortly thereafter.

Embodiment No. 1

A model HDC-3125 tungsten-inert gas (TIG) electric arc welding unit(Hobart Brothers Co., Troy, Ohio) was prepared for use. Specifically,the power level was adjusted such that, during welding, about 70-80amperes DC of electricity flowed through the arc. A commercially pureargon gas flow rate of about 5.9 liters per minute was flowed around anapproximately 0.094 inch (2.4 mm) diameter tungsten-2 weight percentthoria electrode (Teledyne Wah Chang Huntsville, Huntsville, Ala.). Theelectric arc was struck by briefly contacting the electrode to a metalwork table which supported the assembly 208 comprising the compositebody 200 and the titanium alloy sheet 202 and which was electricallyconnected to the positive side of the circuit. The arc was quickly movedto approximately the point indicated as number 206 near one edge of thecomposite body 200 to heat the assembly and particularly the region nearseam 204. The electrode was positioned about 1/32 to about 1/16 inch(0.8-1.6 mm) above the surface of the composite body 200. After a fewseconds, the composite body had heated sufficiently to permit the arc tobe moved closer to seam 204 to further heat the titanium alloy sheet202. In a matter of a few more seconds, a small pool of molten materialfrom titanium alloy sheet 202 had formed and wet the composite body 200at seam 204. The electrode was then moved slowly along seam 204, tocreate additional molten material and to manipulate said molten materialinto seam 204, substantially filling and eliminating said seam. Afterthe electrode had been moved substantially completely along seam 204,the electrical circuit was interrupted, collapsing the arc. The weldingtorch was held over the last point on the weld line for several secondsso that the argon gas sheath would prevent oxidation of this lastportion of the weld to cool. The assembly was then allowed to cool inair.

Embodiment No. 2

After the assembly 208 had cooled in air to a temperature below about700° C., a joining operation was then attempted along the opposing seam210. The procedure described in the preceding paragraph wassubstantially repeated except that material from a metal welding rod(similar to the welding rod shown as 226 in FIG. 28) comprising byweight about 6% aluminum, 4% vanadium and the balance titanium andmeasuring about 15 inches (381 mm) long by about 1/16 inch (1.6 mm) wideby about 0.042 inch (1.07 mm) thick was also heated and melted by theelectric arc to produce a fillet 212 as shown schematically in FIG. 26.The assembly 208 was permitted to cool in air back to approximately roomtemperature.

The joined assembly 208 was sliced using EDM to expose a cross-sectionof the joints, which was subsequently mounted and diamond polished forfurther study.

FIGS. 27a and 27b are, respectively, photographs of the fillets (weldlines) indicated in FIG. 26 as 214 and 212. FIG. 27a shows that aportion of the titanium alloy sheet 202 melted, wet the adjacentcomposite body 200 and filled in seam 204 between the sheet and thecomposite body. FIG. 27b shows that the welding rod material and aportion of the titanium alloy sheet 202 melted, wetting the compositebody 200 and substantially filling in seam 210 between the alloy sheetand the composite body.

Thus, this Example demonstrates that a platelet reinforced compositebody may be joined to a metal comprising titanium using various weldingtechniques. Additionally, this example also demonstrates that a weldingrod material may be employed to increase the size of the fillet at thewelding surface.

EXAMPLE 13

This Example demonstrates the joining of one platelet reinforcedcomposite body to a second platelet reinforced composite body utilizingelectric arc melting of a welding rod material which is capable ofwetting the platelet reinforced composite bodies. FIG. 28 is across-sectional schematic view of the configuration of the plateletreinforced composite bodies utilized in the joining operation describedbelow. The platelet reinforced composite bodies were formed insubstantially the same manner as was employed in fabricating the bodiesdescribed in Example 12.

Referring to FIG. 28, a first platelet reinforced composite body 220measuring about 1.7 inches (43 mm) long by about 1.45 inches (37 mm)wide by about 0.4 inch (10 mm) thick was placed against a secondplatelet reinforced composite body 222 having substantially the samedimensions as the first platelet reinforced composite body such that thelong edge of the first body was in substantial conforming engagementwith the long edge of the second body, with the contact area definingseam 224.

The equipment and procedures employed in the present Example weresubstantially the same as those described in Embodiment 2 of Example 12with the exception that prior to introducing the previously describedtitanium alloy welding rod 226, the first body 220 and second body 222were preheated with the electric arc at a location above seam 224 asindicated by number 228 in FIG. 28.

After cooling the joined assembly to a temperature substantially belowabout 700° C. the joined assembly was inverted so as to permit theformation of a second bond along line 230 in substantially the samemanner as was used to form the first bond along line 228. After theformation of the second bond, the joined platelet reinforced compositebodies were permitted to cool in air back to approximately roomtemperature.

FIG. 29 is a photograph of the joined platelet reinforced compositebodies and shows that the titanium alloy welding rod material wetted andjoined the two platelet reinforced composite bodies and partiallypenetrated the seam between the two bodies.

Thus, this Example shows that two platelet reinforced composite bodiesmay be joined to one another by using an electrical welding apparatus tocontact the seam between the bodies to be joined with a molten titaniumalloy under welding conditions and permitting the molten metal to wetand bond to a portion of each body along the seam.

EXAMPLE 14

This Example is similar to Example 2 in that it demonstrates that twoplatelet reinforced composite bodies may be joined to one another byheating said bodies to a semi-liquid state. In the present Example,however, the two bodies are contacted against one another under very lowpressure. FIG. 30 is a cross-sectional schematic view of the lay-up usedin fabricating the platelet reinforced composite bodies. FIG. 31 is across-sectional schematic view of the apparatus used in joining theplatelet reinforced composite bodies to one another.

A preform comprising boron carbide was fabricated in substantially thesame manner as was the preform described in Example 4 with the exceptionthat the graphite mold into which the slurry comprising the boroncarbide particulate was sediment cast corresponds to that shown in FIG.30.

Referring to FIG. 30, a Grade AGSX graphite rod 236 (Union CarbideCorp., Carbon Products Division, Cleveland, Ohio), measuring about 1/2inch (13 mm) in diameter by about 3.25 inches (83 mm) long, was cleanedin ethanol and adhered to the center of the floor of a Grade ATJgraphite mold 238 (Union Carbide Corp.) measuring in its interior about3 inches (76 mm) square by about 3.25 inches (83 mm) high with a thinlayer of RIGIDLOCK® graphite cement (Polycarbon Corp., Valencia,Calif.). The bonded graphite mold 238 and rod 236 were then placed intoan approximately 120° C. drying oven and dried in air for about 3 hours.

The sediment cast boron carbide preform 50 was dried in substantiallythe same manner as was the preform of Example 4.

The graphite mold 238 and its contents were then heated to a temperatureof about 670° C. to remove the binder material from the sediment castpreform. The heating was substantially the same as that described inExample 4 except that instead of maintaining a flowing argon gasatmosphere as described in Example 4, the entire heating schedule wasdone under a vacuum of at least about 30 inches (762 mm) of mercury.After the graphite mold 238 and its contents had cooled back tosubstantially room temperature, the weight of the mold and its contentswas recorded, which revealed that the preform 50 had a mass of about 149grams. The thickness of the preform was about 0.77 inch (20 mm).

About 1227 grams of nuclear grade zirconium sponge parent metal 54(Western Zirconium Co., Ogden, Utah) was poured into the graphite mold238 on top of the sediment cast boron carbide preform 50 and leveled toform a lay-up. The lay-up was then placed into a vacuum furnace andheated in substantially the same manner as was the lay-up described inExample 4 with the exception that the second evacuation reduced thevacuum chamber pressure to about 2×10⁻⁴ torr. Also, upon completion ofthe approximately 2 hour dwell at a temperature of about 1950° C., thefurnace and its contents were cooled to a temperature of about 1400° C.at a rate of about 75° C. per hour and further cooled from a temperatureof about 1400° C. to about room temperature at a rate of about 274° C.per hour. When the furnace temperature had reached about roomtemperature, the lay-up was removed from the furnace. The contents ofthe graphite mold 238 were removed from the mold to reveal that thezirconium parent metal 54 had infiltrated and reacted with the boroncarbide preform 50 to produce a platelet reinforced composite bodycomprising zirconium diboride, zirconium carbide and about 22 volumepercent of residual unreacted parent metal as determined by quantitativeimage analysis (described previously in Example 6).

Two such formed platelet reinforced composite bodies were machined intothe shape of a tube, each approximately 1 inch (25 mm) outside diameterby about 0.65 inch (16.5 mm) inside diameter by about 1.375 inch (34.9mm) long, using electro-discharge machining (EDM). The residual EDMdebris was removed by sandblasting. One end of each tube was diamondpolished to help achieve good contact between the ends of the tubesduring the subsequent bonding operation.

Referring to FIG. 31, a first platelet reinforced composite tube 240 wasplaced onto a Grade AGSX graphite support plate 242 measuring about 5inches (127 mm) in diameter by about 0.25 inch (6 mm) thick with thepolished end of the tube facing up. The second platelet reinforcedcomposite tube 244 was then placed on top of the first tube 240 with thepolished end of the second tube contacting the polished end of the firsttube and in substantial conformity therewith. The two plateletreinforced composite tubes 240, 244 thus shared a common axis. A GradeAGSX graphite pressure plate 246 having substantially the samedimensions as the support plate 242 was then placed on top of the secondplatelet reinforced composite tube 244 to help maintain the first tube240 and the second tube 244 in place during the subsequent heatingprocess. The pressure applied to the contact area 256 between tubes 240and 244 amounted to about 1.5 psi (10 kPa). The graphite pressure plate246 was in turn maintained in a relatively fixed position with GradeAGSX graphite dowel rods 248 and alignment guides 250. A quantity ofnuclear grade zirconium sponge 252 (Western Zirconium, Ogden, Utah) wasplaced on the support plate 242 near the first tube 240 in an effort toremove any impurity oxidizing gases from the formed assembly 254.

The assembly 254 and its contents were then placed into a retort. Theretort chamber was sealed from the external environment and the chamberwas evacuated to a vacuum of about 30 inches (762 mm) of mercury andthen backfilled with argon gas to about atmospheric pressure. The retortwas evacuated a second time using a mechanical roughing pump to a vacuumof about 30 inches (762 mm) of mercury, after which a high vacuum sourcewas connected to the retort chamber to further evacuate said chamber toa reduced pressure of about 3×10⁻⁵ torr. After checking for vacuumleaks, power to the heating elements of the retort was applied and theretort chamber and its contents were heated from about room temperatureto a temperature of about 1000° C. at a rate of about 243° C. per hour.Upon reaching a temperature of about 1000° C., the high vacuum sourcewas isolated and the retort chamber was backfilled with commerciallypure argon to a pressure of about 2 psig (14 kPag). An argon gas flowrate through the retort of about 2 standard liters per minute wasthereafter established. The retort and its contents were then heatedfrom a temperature of about 1000° C. to a temperature of about 1800° C.at a rate of about 200° C. per hour. After maintaining a temperature ofabout 1800° C. for about 2 hours, the temperature was reduced to atemperature of about 1400° C. at a rate of about 100° C. per hour. Froma temperature of about 1400° C., the temperature was further reduced ata rate of about 250° C. per hour. After the retort and its contents hadcooled to substantially room temperature, the retort chamber was broughtback to atmospheric pressure and opened. The assembly 254 was recoveredfrom the retort chamber and disassembled to reveal that the two plateletreinforced composite tubes 240, 244 had bonded to one another.

FIG. 32 is a photograph of the bonded tubes before any finishingoperations were performed.

The bonded tubes were EDM machined such that the overall joined tube hadnearly the same inside and outside diameters as the initial, individualcomponent tubes and had an overall length of about 2.4 inches (61 mm).No cracks or voids, particularly at the contact area 256, were revealed.

FIG. 33 is a photograph of the bonded tubes after the machining step.

This Example therefore demonstrates that platelet reinforced compositebodies may be bonded to one another simply by contacting the bodies(under nominal external pressure) and heating to a sufficienttemperature in an inert atmosphere.

We claim:
 1. A method for producing a self-supporting body,comprising:providing at least one first self-supporting body which ismade by a process comprising (i) heating a parent metal in asubstantially inert atmosphere to a temperature above its melting pointto form a body of molten parent metal; (ii) contacting said body ofmolten parent metal with a permeable mass which is to be reactivelyinfiltrated; (iii) maintaining said temperature for a time sufficient topermit infiltration of molten parent metal into said permeable masswhich is to be reactively infiltrated and to permit reaction of saidmolten parent metal with said permeable mass to form at least onecompound selected from the group consisting of a parent metalboron-containing compound, a parent metal carbon-containing compound anda parent metal nitrogen-containing compound; (iv) continuing saidinfiltration reaction for a time sufficient to produce said at least onefirst self-supporting body; contacting said at least one firstself-supporting body with at least one second self-supporting body;heating said at least one first self-supporting body and said at leastone second self-supporting body to at least the melting point of atleast one portion of said at least one first self-supporting body; andmaintaining said contacting at said temperature for a time sufficient tobond said at least one first self-supporting body to said at least onesecond self-supporting body.
 2. A method for producing a self-supportingbody, comprising:providing at least one first self-supporting body whichis made by a process comprising (i) heating a first parent metal in asubstantially inert atmosphere to a temperature above its melting pointto form a first body of molten parent metal; (ii) contacting said firstbody of molten parent metal with a permeable mass which is to bereactively infiltrated; (iii) maintaining said temperature for a timesufficient to permit infiltration of molten parent metal into saidpermeable mass which is to be reactively infiltrated and to permitreaction of said molten parent metal with said permeable mass to form atleast one compound selected from the group consisting of a first parentmetal carbide and a first parent metal nitride (iv) continuing saidinfiltration reaction for a time sufficient to produce said at least onefirst self-supporting body; providing a material which is to bereactively infiltrated on at least a portion of a surface of said firstself-supporting body; contacting said material to be infiltrated with atleast one second self-supporting body; contacting said material to beinfiltrated with a second molten parent metal for a time sufficient topermit infiltration of said molten parent metal into said material to bereactively infiltrated and to permit reaction of said second moltenparent metal with said material to form at least one compound selectedfrom the group consisting of a second parent metal boron-containingcompound, a second parent metal carbon-containing compound and a secondparent metal nitrogen-containing compound; and continuing saidinfiltration reaction for a time sufficient to bond said at least onefirst self-supporting body to said at least one second self-supportingbody.
 3. A method for producing a self-supporting body,comprising:providing at least one first self-supporting body which ismade by a process comprising (i) heating a parent metal in asubstantially inert atmosphere to a temperature above its melting pointto form a body of molten parent metal; (ii) contacting said body ofmolten parent metal with a permeable mass which is to be reactivelyinfiltrated; (iii) maintaining said temperature for a time sufficient topermit infiltration of molten parent metal into said permeable masswhich is to be reactively infiltrated and to permit reaction of saidmolten parent metal with said permeable mass to form at least one parentmetal nitrogen-containing compound; (iv) continuing said infiltrationreaction for a time sufficient to produce said at least one firstself-supporting body; providing a brazing material on at least a portionof a surface of said first self-supporting body; contacting said brazingmaterial with at least a portion of a surface of at least one secondself-supporting body; heating said at least one first self-supportingbody, said brazing material and said at least one second self-supportingbody to a temperature which permits the brazing material to bond said atleast one first self-supporting body and said at least one secondself-supporting body together.
 4. A method for producing aself-supporting body, comprising:providing at least one firstself-supporting body which is made by a process comprising (i) heating afirst parent metal in a substantially inert atmosphere to a temperatureabove its melting point to form a first body of molten parent metal;(ii) contacting said first body of molten parent metal with a permeablemass which is to be reactively infiltrated; (iii) maintaining saidtemperature for a time sufficient to permit infiltration of moltenparent metal into said permeable mass which is to be reactivelyinfiltrated and to permit reaction of said molten parent metal with saidpermeable mass to form at least one compound selected from the groupconsisting of a first parent metal boron-containing compound, a firstparent metal carbon-containing compound and a first parent metalnitrogen-containing compound; (iv) continuing said infiltration reactionfor a time sufficient to produce said at least one first self-supportingbody; providing a material which is to be reactively infiltrated on atleast a portion of a surface of said first self-supporting body;contacting said material to be infiltrated with at least one secondself-supporting body; contacting said material to be infiltrated with asecond molten parent metal for a time sufficient to permit infiltrationof said molten parent metal into said material to be reactivelyinfiltrated and to permit reaction of said second molten parent metalwith said material to form at least one compound selected from the groupconsisting of a second parent metal carbide and a second parent metalnitride; and continuing said infiltration reaction for a time sufficientto bond said at least one first self-supporting body to said at leastone second self-supporting body.
 5. The method of claim 1, wherein thecomposition of said at least one first self-supporting body issubstantially identical to the composition of said at least one secondself-supporting body.
 6. The method of claim 1, wherein said at leastone first self-supporting body has a composition which is different fromthe composition of said at least one second self-supporting body.
 7. Themethod of claim 1, wherein said parent metal comprises at least onemetal selected from the group consisting of zirconium, titanium andhafnium.
 8. The method of claim 1, wherein said permeable mass which isto be reactively infiltrated comprises at least one material selectedfrom the group consisting of a carbon source material, a boron sourcematerial and a nitrogen source material.
 9. The method of claim 1,wherein said at least one first self-supporting body further comprisesan inert filler material.
 10. The method of claim 1, wherein externalpressure is applied to at least one surface of said at least one firstself-supporting body, said at least one second self-supporting body orboth, so that pressure is applied at least one surface where said atleast one first self-supporting body contacts said at least one secondself-supporting body.
 11. The method of claim 1, further comprisingproviding a substantially inert atmosphere during said heating andmaintaining steps.
 12. The method of claim 2, wherein the composition ofsaid at least one first self-supporting body is substantially identicalto the composition of said at least one second self-supporting body. 13.The method of claim 2, wherein said at least one first self-supportingbody has a composition which is different from the composition of saidat least one second self-supporting body.
 14. The method of claim 2,wherein said first parent metal comprises at least one metal selectedfrom the group consisting of zirconium, titanium and hafnium.
 15. Themethod of claim 2, wherein said at least one first self-supporting bodyfurther comprises an inert filler material.
 16. The method of claim 2,wherein said first parent metal has a composition substantially similarto the composition of said second parent metal.
 17. The method of claim2, wherein said first parent metal has a composition different from thecomposition of said second parent metal.
 18. The method of claim 2,wherein said material which is to be reactively infiltrated furthercomprises an inert filler material.
 19. The method of claim 3, whereinexternal pressure is applied to at least one surface of said at leastone first self-supporting body, said at least one second self-supportingbody, or both, so that pressure is applied at least one surface wheresaid at least one first self-supporting body, said brazing material andsaid at least one second self-supporting body are in contact.
 20. Themethod of claim 3, wherein said brazing material is supplied to at leastone seam between said at least one first self-supporting body and saidat least one second self-supporting body after said at least one firstself-supporting body and said at least one second self-supporting bodyare in contact with one another so as to create said at least one seam,and utilizing conventional welding or brazing techniques to melt saidbrazing material to form molten brazing material which is in contactwith at least a portion of said at least one seam and thereafter coolingsaid molten brazing material to form a bond between said at least onefirst self-supporting body and said at least one second self-supportingbody.
 21. The method of claim 3, wherein at least a portion of said atleast one second self-supporting body comprises said brazing material.22. The method of claim 4, wherein the composition of said at least onefirst self-supporting body is substantially identical to or differentfrom the composition of said at least one second self-supporting body,said parent metal comprises at least one metal selected from the groupconsisting of zirconium, titanium and hafnium, and said permeable masswhich is to be reactively infiltrated comprises at least one materialselected from the group consisting of a carbon source material, a boronsource material and a nitrogen source material.